I just think the basic assumption is that they'll produce all three but you're right Gipetto, they have only announced Spider-Man 3 as the licence they hold and it also happens to give them the most characters to choose from: Spidey, Black Spidey, Sandman, Venom, Green Goblin 2. More bang for their licencing buck you could say.
That's the only reason I an see why they chose Spiderman 3 and not one of th others. the first two were better IMO but I'm still glad we're getting a Spidey nonetheless.
And it would he nice if like EVILFACE said, they actually hold all 3 licenses