Series rules have been broken before.
He doesn't fly, but he can "leap tall buildings in a single bound" - literally, he jumps - no actual horizontal flight, just vertical jumping. It's rarely used though. I think I can count how often on one hand.
The real reason for the lack of the suit at this point is legality. Which is really a cop-out for DC and WB. Truth is, they either think people too dumb to accept two people playing Supes, or they're just being idiots.
Though there has also been rumor for all these years that Welling is a believer in the Superman curse, and thus is the reason he's had it guaranteed to him he'll never have to don the suit.
If anyone is dumb enough not to be able to accept Welling on TV in the suit, while simultaneously accepting another actor in the suit in films... they should be euthanized.
Everyone who had watched this show wants just one damn thing: Welling, in the suit, atop the Daily Planet, before flying off to the triumphant fan-fare for the final 30 seconds of the damn series.
That's it. That's all we want. It's not asking a lot, is it? They've boned us around for years. This show was supposed to be a 4-year high school only show. Then they said, "one more" to wrap it up. And then it snow-balled like a shit-storm. This show was supposed to end every year for the past 4 seasons. This year it looked definite, and again, it looks to get a likely reprieve.
Which is fine, it's a good show. But it's screwed with us, toyed with us, teased us, and pissed us off a lot. We deserve our reward for years of faithful viewing and buying DVDs and enduring so many soap opera moments. We deserve 30 damned seconds of "awesome" with him finally being Superman and flying off towards his much-talked-about destiny.
If we don't get it, it's a worse "fuck you" to the fans than the ending of Enterprise.