I know that seems like blasphemy to die hard comic fans, but here is my logic. The Avengers will put up huge numbers at the box office. I'm talking Pirates of The Caribbean, Transformers type money. I fully expect this movie to make a billion dollars worldwide. Now, the people at Disney are very, very smart at making money, and they know nobody outside of hardcore comic fans are really clamoring for a Thor or Cap sequel. Let's be real, they are B-list characters anyway, and while the movies did well at the box office, they didn't exactly set the world on fire, nor got many people talking. The only reason we were treated to a Cap and Thor movie was to set up Disney and Marvel's next cash chow The Avengers. But, put them on a team with Iron Man and Hulk, and suddenly they are A list.
I fully expect at the end of the summer when the Avengers run at the box office is all but done, Disney will announce that the next two Avengers movies will be shot back to back (a la The Pirates of the Caribbean sequels), and be released in 2014 and 2015 respectively. They will sit out 2013 all together, which in the long run I believe will result in more money being made. Disney is too smart to over saturate the market with B list super hero movies, when they can make so much more money fast tracking two Avengers movies, which the majority of people care more about anyway.
Also, from a competition standpoint an Avengers movie will make much more money for Disney then releasing solo flicks. Remember after this year Batman will take at least a five year hiatus, a Superman sequel won't be released until 2016 at the earliest, and yes, no twilight films either. The competition will be quite weak, and an Avengers sequel could make more than the first movie easily because of that. The only comic book movie that could compete with it would be a First Class sequel and anything with the name Spider man in it. Also, if this movie receives good reviews, and gets people talking (I'm expecting an 85% tomatometer rating), then anticipation for a sequel will be quite high, and with no competition the movie would make a killing.
Now, and this is my just my personal opinion, I would love for more Avengers movies than solo movies starring Cap, Thor and even Iron Man. I just think that the quality of The Avengers movies will be much higher.
I also think Disney and Marvel will look to make solo films for Cap and Thor after 2015, although, who knows what properties they could have by then?