I see these same arguments everywhere I go. *sigh*
Clearly, TW does not want to wear tights... ON SMALLVILLE. He's made that clear in interviews, and people close to him (castmates, crew, etc.) would know that. Some of his friends have short memories however (I'm looking at you, Allison), because the "no tights, no flights" rule was SOLELY G&M's concept from the very beginning, LONG before they ever heard of a dude named Tom Welling. There's copious articles to back that up. Do a Google search folks, read the compendiums; the truth is out there.
The show isn't about a grown-up Superman. TW did NOT sign up for that, and he's said in interviews he'd never allow it. This is where the contract stipulation comes in. Having the no tights contract clause is reassuance that the show will always be about Clark Kent. Because once the tights appear, you can count the seconds to the ending credits; that's it, game over.
Now, this stuff ^ is applicable to SMALLVILLE only! Only thing he's ever said about a Superman FILM is that he wouldn't want to do a remake. (Humorous considering the SR requel.) Nobody here knows how Welling feels about playing Superman in a new film. NOBODY! Furthermore, you can't take statements he's made about wearing a skin-tight OW-fit on a television show and extrapolate them into an "ixnay" on a multi-billion dollar film franchise. C'mon people.
Is it Thursday yet?