There have been other games far bigger than this. A lot of comparables can be seen here (http://i.imgur.com/uBWCz.jpg) and here (http://www.actionradius.com/jdl/default.asp?id=1801&qty=1).
Most notable is Far Cry 2 in my opinion, which is an FPS-game. Very big and quite impressive to be twice as big as Skyrim/Oblivion for being a game like that, in my opinion.
Red Dead Redemption (not on the links above) is also worth mentioning. Roughly 72 square kilometers as far as I know, making it almost twice as big as Skyrim/Oblivion, while still being an open-world RPG as well.
You can't forget to mention Just Cause 2 as well. 400 square kilometers. And it all looks amazing. Very impressive indeed.
1. We know Skyrim is "about the same size as Oblivion". We don't know if it's more, exactly the same or less. But if you were a developer today, would you say that your new game was smaller than your previous one? No, you wouldn't. You would most likely say that it's "about the same size" or something like that. If your new game was somewhat bigger than your old game, you would also as a developer naturally say that, as that's something good. This gives us the question if Skyrim is actually even a bit smaller than Oblivion.
2. The importances of a big game world are many. There are many things that an open-world game like TES would benefit from it. Let me count up a small list:
A) The world doesn't risk feeling cramped up. This is a very important thing imo. Oblivion did feel very cramped up in my opinion, like if someone had tried to stuff as much as possible in a compact world space. There were dungeons everywhere and you couldn't miss finding one every 30 seconds during your exploration. This hurts the immersion and hurts the feeling of exploration in my opinion. While Skyrim got less dungeons, the risk is still there. Mountains take up a lot of space, and cities are also (supposedly) much bigger now. There are also somewhat 20 towns/villages. If Skyrim feels cramped up, this is a very very bad thing.
B] You will never be able to experience great majestic mountains and valleys and other landscapes, without them getting ridiculously scaled. Oblivion's big Imperial valley looked very impressive at first, but when I finally got around running I noticed how small it actually was. Barely took any time at all to cross it. Skyim's landscapes does look impressive so far, but will they be ridiculously scaled? Yes. They have to be ridiculously scaled if they are to fit within 41 square kilometers, like in Oblivion.
You can say good-bye to landscapes like this:
http://www.wallpaperpimper.com/wallpaper/Landscape/Landscape/Valley-Vista-1-RP6ONRV6I8-1600x1200.jpg
http://hd-wallpapers-widescreen.thundafunda.com/plog-content/images/wallpapers/landscape-wallpapers-pictures/amazing-green-mountains-with-trees-lanscape-wallpaper.jpg
http://www.ashevilleguidebook.com/wnc/images/Fall%20in%20the%20mountains.jpg
http://www.wallpaperden.com/pics/majestic-spring-valley-3.jpg
http://images.nationalgeographic.com/wpf/media-live/photos/000/133/cache/colorado-mountains-earthscapes_13329_990x742.jpg
A good measurement is trees. Trees are always the same size, pretty much. And their size can't fool you. When you see far-looking image over a "huge" landscape, look on the tree size. How big are the trees in the distance?
We will definitely notice the world being ridiculously scaled when we play the game ourselves, or see some real footage (without interruptions). Running through a big-looking valley (at first sight) will most likely go by now time, like in Oblivion.
C) The world can be filled more realistically with different things. Things can be more realistically spread out. The world can be done faster, but still made unique. This has a lot to do with point A) where I stated how the world can risk feeling cramped up.If someone make a big world and spread out all the dungeons, towns, cities, locations of interest, etc... then it doesn't require as much work to accomplish this huge world, while the world also feel more realistic and less cramped up. You'll no longer find a dungeon every 30 seconds.
That leaves us with the problem of all this vegetation and such. All the trees, bushes and other foliage. That will take time to place, yes? Yes it will, as it would always. But the time can be shortened considerably by using something like Far Cry 2 used here: http://www.youtube.com/watch?v=C8qa-naczjg&feature=player_detailpage#t=63s
I prefer to call it "random handcrafting". You don't need to place every bush carefully, as long as you have a decently written tool like this. It would make world editing much faster and easier.
This is all a good start, but what about unique landscapes? Skyrim has a lot of those now. This is great and important. Landscapes are supposed to feel unique and not too bland. My idea is that you start with what I said above, but then of course handcraft the game world to be unique on a lot of places like Skyrim probably has already.
D) Huge landscapes have a value of itself. Huge landscapes have a feeling to them that can never be replaced by a smaller landscape. TES-games have always been these open and free worlds. I was a bit disappointed with the size of Oblivion after I finally played it through. It suddenly felt so small. I then discovered the mod MERP (http://www.tesnexus.com/downloads/file.php?id=29214), which is a LOTR-mod that take place in Middle-earth, but where the world is over SEVEN times bigger than original Oblivion. When I played this mod (still unfinished) it felt so great to be in such an amazingly huge world. Valleys and mountains that looked big actually now also felt and were big. It was truly amazing.
3. After reading all of the above, do you feel disappointed with Skyrim's world size being "about the same as Oblivion's"?
I personally do. I have a fear of Skyrim feeling cramped up and of Skyrim feeling ridiculously scaled once you actually play it. I also fear I won't be able to feel that great feeling of huge landscapes that I felt in the LOTR-mod for Oblivion (MERP). But you have to value the amount of work it requires to accomplish this huge world. I personally think 70-80 square kilometers would be perfect for Skyrim, rather than ~41 square kilometers.
4. Do you hope for the next BGS game (Fallout 4 or TES 6) to be bigger?
This is the most relevant question. Skyrim is done and nothing can be done about the world size now.
I personally hope the next BGS game to be bigger, mainly for all the reasons stated above.