» Fri Feb 11, 2011 2:03 am
For the statements that there can only be 20 dragons, because there are only 20 shouts:
"Over time, players will build a vast arsenal of shouts: over 20 complete shouts in all, each with multiple words that must be gathered from different places around the world. “There are three words for each shout, and there are three levels to them. The amount of time you hold down the shout button is how many words come out,” Howard continues. “It becomes a bit of a collection mechanic – to collect all the words.”" - http://www.gameinformer.com/b/features/archive/2011/01/20/skyrim-s-dragon-shouts.aspx
"I honestly don't know the exact number yet. Some are scripted to appear at certain times, and some are completely random. We're currently messing with that number, and it also depends on how you play the game. I got randomly hunted by three of them at once in the game last week, and I assure you that's too many at once. I can guess a low number of maybe a dozen, and a high number many multiples beyond that. Theoretically it's infinite I guess, since we put them in the world like any other creature. We went into the project being very conservative about how we'd use them, but they've turned out great, so we want them to get good screen time. When you defeat a dragon, you absorb its soul, and that's all I should say about that for now. " - http://pc.ign.com/articles/115/1158651p1.html
So, no, there are not only 20 dragons - No one, not even Todd Howard knows how many dragons there are, so it's very much undecided. (Though, as of now, there are infinite dragons, as they spawn like any other creature.)