At least with Strider's appearance it was somewhat understandable why they couldn't get him in the game at first; he's not quite just Capcom's character. He also has partial ownership by Moto Kikaku, a group of manga artists who wrote the Japanese exclusive manga series. It's more or less the same reason why Nintendo cannot use characters like Geno and Mallow in future Mario games, because they need permission and copyright approval by Square-Enix, the company who helped develop Super Mario RPG.
You can change his voice to his Japanese one, ya know. If the English dub bothers you so much. At least you can with the original MvC3.
Now that you mention, I'm not sure why Gambit and Jin haven't made an appearance either. Jin's a pretty obscure character, so that's understandable at least (but yet he's replaced with other obscure characters, so I dunno...), but Gambit is a extremely popular X-Men character.
_________________ The Local Video Gaming Lunatic
Recent stuff I'm into:
Watching: A Certain Scientific Railgun (ep.14, stalled), Hoshi no Kirby (ep. 71, stalled), Nazo No Kanojo X (ep. 8), Acchi Kocchi (ep. 8)
Reading: nothing