The number of blocks each one occupies is almost definitely the rough size of the settlement. Assuming the map is probably larger than Cyrodill, that means MUCH more area covered. What about the map makes it look small? It's just a drawing, the mountains are not actually that size and shape.
That's a lot of assuming.
What makes it look small is the space between these settlements/points-of-interest markers; in comparison to Morrowind or Oblivion it looks incredibly sparse. Hopefully these are only marking major cities and towns, not villages, dungeons, etc, although why those wouldn't be on the map I have no idea, unless they took them down for the BTS shoot so not everything was given away. if only we could clearly see the marker legend on the side of the map, then we'd know for sure.
Hopefully in reality it is more like this:
http://images4.wikia.nocookie.net/__cb20090123084948/oblivion/images/thumb/e/e2/OblivionMapAGM_v1_1.jpg/815px-OblivionMapAGM_v1_1.jpg
and this:
http://images.g4tv.com/ImageDb3/166167_S/The-Elder-Scrolls-II-Daggerfalls-Map-Is-62-Square-Miles----Hows-That-Compare-To-Oblivion.jpg