Originally Posted by Mr. Dent
Joss never said Thanos wouldn't be in Avengers 2. In fact he pretty much said he would be. :/
He said Thanos is someone you save for the "big finale." I don't think Avengers 2 is intended to be the big finale of Marvel's franchises.
You also can't up the ante behind Thanos. If Thanos is in Avengers 2, they have nowhere to go but down for Avengers 3.