Do they literally have to play the game through every single area you can go in and see if it's all working, with a game this big wouldn't that take months of non-stop playing? They'd have to listen to every line of dialogue to see if it is all working properly, and other stuff like that.
I think it's understandable they may miss a couple of bugs here and there with a game world so massive as Skyrim.
I know it would in reality be a lot more technical than this though, can anyone explain how they do it?

Bethesda Softworks hires a couple hundred people to do QA testing. My quest mods are only like 3-7 hours and I had at least 5-10 people play through each one. I can only imagine with 500 hours of content they would have a couple hundred people.

They are bug testing now. Vsions said he's been constantly play testing lately.

I heard/read in one of the interviews that they have a program that they leave running during the night, which performs preprogrammed sets of actions repeatedly until the game crashes. Then, the devs find out (through some error log, no doubt) what cause the error and fix it. for other bugs like floaters/ miscellaneous errors, they use play testers (often including themselves).

i believe they do this certain thing so say a dungeon in the mountains they go through that 100's of times until they're bored of it then they do it another hundred if they find a bug they remove it then repeat that in the same dungeon 100's to make sure it doesn't happen and there isn't anymore.

might not be the exact way but im sure its close

What I wonder is how it works across various versions. Do they playtest the individual versions for bugs or mostly only that of the lead platform while assuming the bugs and fixes carry over to the others?

Well I think they have Development Builds and tree of commits and bug report system similar to this one for example or maybe in for of wiki.
https://crawl.develz.org/mantis/view_all_bug_page.php
Patching ESM with commits I believe.

The Making of Oblivion had a section on Bug Testing, and they do infact go into every area and try dozens of things to make sure everything works fine.

That sounds probable. They probably write automated tests for some of the lower level physics type operations and play test for the more complicated quests and interactions.

Most bugs in Skyrim.ESM, I'd imagine, if fixed for one platform would be fixed for the others. The scripting is the most likely place for problems to arise, or at least it has been in previous games, so altering a script in one build fixes all. That doesn't take into account the number of other bugs that can arise, like bad .NIFs or pathing errors, but by the same token, fixing any given form/asset would probably carry over across all platforms. The .exe or whatever the platforms use, however, is probably more specific as there are bound to be unique limitations and pitfalls for each platform. Something that always crashes on PS3/XBox might not be a problem at all on PC or visa versa. Admittedly, I've only bughunted/fixed for PC, so I could quite possibly be wrong about the .exe stuff. I'm fairly confident the ESM assertions are correct though.

Do the consoles have .ini files? I know they're not user editable if there are, but that's another potential platform specific element of the fugbixing process.