I doubt that it will but here are a few points; The game is small enough to run in one disk (compared with other new big games running in two or three disks on Xbox 360 like Rage for example) Even for a 3.8 GB size and especially a 2 hour and 15 minute
speedrun to beat the game (if you were a developer) It would be either that or the game may be filled with many bugs but I don't blame it, with the amount of things that you can and will do.
The main story line is bound to be short. It always is, what adds to the longevity to the game are the side quests and various factions and everything and Skyrim will not be short. A small install size does not determine how long a game is. Any developer
can tell you that they can reuse textures(which is something Bethesda does and has coonfirmed they have done with Skyrim) which results in smaller sizes.
I wouldn't worry OP. The worst thing is that the game may in fact be buggy at times. Oblivion was like this and it lasted people hundreds, even thousands of hours. They have a system planned out for finding and fixing
In regards to some of your points: I don't think I've ever seen an open world RPG (or any game, for that matter) divided up. That wouldn't work well. Insert disc 2 to fast travel to the other half of the map?
The game had a fast speed run. True. Oblivion's speed run time wasn't much slower. Either way, the story is the last thing I plan on doing.
3.8 GB install may not seem like much but it wouldn't matter. With a map about the same surface area as Oblivion and with even more points of interest, the game is not small.