Ladiez and Gontelmenz,
I just read an article that I found from a Steam link. PC Gamer wrote an article from a reddit crowdsourced interview of Cliff Bleszinksi (apparently he's quite a well known guy in the game industry.) He said some very interesting things:
1. He loves the idea of an open world Unreal (I do as well - what an incredibly good idea)
2. Skyrim absolutely blew him away (same for me)

The reason I mention the article is that he points out something that should be obvious, but is easily overlooked or ignored by most folks (including me.) There's tons of growth in the game industry, and all the major game houses are severely understaffed for the demand - both for support and developing new titles. He also points out that the mod ecosystem has exploded, for obvious reasons.

So what does that tell me? The conclusion is inescapable.
We're going to see an endless supply of mod content for Skyrim. Additionally, I'd say it's near guaranteed that Bethesda will develop a significant number of DLC's and expansions as well - more than the 3-5 they originally estimated.
This is a $1B franchise and counting. Even if Bethesda were to develop an expansion that was, say, 25% of the size of Skyrim (which is already gigantic - consider that it takes at least 300 hours for even fast players to complete all quests in the game, we're talking about an expansion of 75 hours MINIMUM), and only appealed to 25% of the audience (a ridiculously low estimate), it would still be a $250M value to Bethesda. Furthermore, it would be based on an already existing platform/vehicle/engine, and thus VASTLY cheaper than the original Skyrim development. Thus the revenue and profit potential is irresistible.

The math is there, folks. It's pretty hard to argue against it.

I think we can all rest easy with the conclusion that Skyrim will see more DLC's and Expansions than any previous ES title, and they will be significantly larger than what such add-ons used to be pre-skyrim.

Not true. Bethesda may do 2 or 3 more DLCs for Skyrim, but ultimately they will be moving on to work on another new title. Because there has been such growth and demand for gaming in the past few years, your big gaming companies like Bethesda and EA are more interested in launching new titles than developing new content for older games. An older game is not going to draw in new players like a new title will. The numbers are there too.
Case in point would be Dragon Age. With DA: Origins we saw 5 (maybe 4) after release DLCs and then a separate expansion pack. Dragon Age 2 we only have 2 after release DLCs and a few scattered nonessential item packs. Now Bioware has announced DA3 to be expected near the end of 2013.
If anything companies are moving away from extensive DLC. They're chalking most up with day one releases and your expansion packs have ceased to exist.

Don't forget about the upcoming new-generation consoles. Bethesda has to keep up with the times!

WHat makes more money? Expansions/DLCs to preexisting games or brand new games?

New games. When Fallout 3 was released, it made more within the first month than Fallout and Fallout 2 did since they were released. The first one was released in 1997. Fallout 3 made more money in one month than both previous games made over a period of 15 years!

And this is standard operating procedures for single-player games; they make the release, sell a bunch, and then try to squeeze as much as they can via DLCs and expansions before moving onto the next one. This is why DA2 only got two DLCs... it was received so poorly that they were better off abandoning additional content so they can work on ME3/DA3. And a well-received game can only have so much money squeezed out of it before the gaming community gets bored and the cost to develop is not worth what you can get out of it. COULD gamesas make a boatload more DLCS? Sure. But eventually they'll go bankrupt if they do.

Now, if Skyrim was a MMO, I could see this happening. MMOs thrive off of DLC (and Expansions,) if they can survive the first year. Look at Everquest (which predates WoW by about 5 years.) It was released in 1999. It's still going in 2012. Because of DLC content (and subscription fees.)

More skyrim, fallout was horrid

Hang on - read the article (look it up on pcgamer.) Then it'll become clear.
Developing new titles is too expensive. The studios with the really big games like Skyrim will have to pump out more expansions/dlc's or their multi-year revenues become so sinusoidal that they can't maintain staff, which would kill them.

I'm tellin' ya - the economics have changed.