I know it's hard to believe that Capcom would take out Strider, a veteran and popular character from previous MvC games, but in case you still don't believe, here's where the deconfirmation comes from:
Guy sent in word about a Tweet Ryota Niitsuma posted not too long ago explaining that Strider Hiryu would not be a playable character in Marvel vs. Capcom 3.
Here's a translation.
Strider Hiryu is popular overseas as well, we took him out of Marvel vs. Capcom 3, because he didn't fit in with its concept.
http://www.eventhubs.com./news/2010/nov/30/strider-hiryu-disconfirmed-marvel-vs-capcom-3/