A lot of you act as if Bethesda can only do one thing at a time. I promise you that is not the case. It is entirely likely that they are working on all their products simultaneously. It is a very common business practice to have several generations of a product-line already completed and waiting to go. Why the wait? One word - money. The goal of just about every company is to maximize profits. As long as the cash is flowing, a new release will be held. Once the money slows to a trickle, that's when a new release is made. I'll give you an example. My father designs ASICS (application specific Integrated circuits) chips. If you watch TV, you see and hear alot about 3-G telephony networks. And now you hear about 4-G networks. Well, that's alot of bull. My father designed the chips for 3-G networks 15 years ago. Virtually all of the features were available then, but not released. Little by little, each year, new features are released to the unsuspecting public so the company can basically resell the same thing to us year after year. This can be applied to Bethesda as well. All of you who played Oblivion will surely notice that the game engine is practically identical. They didn't spend any time building a new game engine, just modifying an existing one to make Fallout 3. That is the reason why Fallout 3 isn't like the other two. They took what they had an applied it to Fallout 3. Mark my words, after several releases (FO4,5,6, maybe 7) you will see a new game engine. And when that time comes, the game will be totally different again. But until that time, we will only see revisions of the existing games. As long as sales are good with each release (and the company doesn't go belly up like Interplay/Black Isle), you can expect to see a new release of every title.
I agree, what is stated above is correct on my vista, while all of you argue on either TES:V or Fallout 3+, there is one fact you are missing: they were working at fallout 3 and oblvion simultaneously, both released with a 2 year difference.
TES:V, it will come when it will come.
More FO3 DLC, unlikely, they said they're done with DLCs, but who knows?
FO4: Orly? FO3 is not even a year old, releasing FO4 before the game is at least 1.5 year old is a dumb thing to do, hurts marketing, people get tired of Fallout, they will want something new, not the same plot, again!