You know what the difference is between the NFL salary cap (and I believe the NHL cap as well) and the NBA salary cap? You can't go over the NFL salary cap, but for some limited exceptions (such as IR settlements). In the NBA, you just have to pay a fine if you go over it, but given that the revenue from playoff ticketing and such tends to far exceed the tax levied, why wouldn't any owner ignore the luxury tax ramifications? It's not a cap in the NBA so much as it is a slap on the wrist.
If small-market/big-market paradigms are so important to Mark Cuban, then he should be proposing a hard cap for the NBA rather than a soft cap with a luxury tax penalty. I understand that a majority vote of the owners would never pass it, but why wouldn't that system work? I wouldn't mind it being immediate, but seeing as making it immediate would DEFINITELY never pass, I'd say give teams 4 or 5 years from the time the rule is approved so they can get all the big contracts off their books. Then, starting with the first season the rule goes into effect, no mercy. If the cap is $X million, you can't be one penny over the cap. Sure, you're going to have some small-market owners that can't/won't afford that, but by and large you would level the playing field. You might not be able to corral player salaries of the big-name players, but you could certainly limit the Scalabrines of the world from cashing in (not that I have anything against him as a person, but even the most die-hard fans would admit his current contract far exceeds his value.) I'd even be willing to consider allowing minor excursions above the cap to allow for Bird Rights and MLEs (though I'm not sold on that.) People say it doesn't work? Well, the NFL and NHL seem to be doing pretty well with their hard caps.
All that being said, I find it particularly ironic that Mark Cuban is the one going off on the imbalance in salaries and the salary cap. This is a guy who vowed to pay whatever it took to get Shaq to Dallas, a guy who has spent hundreds of millions by now to upgrade every element of his facilities, buses, planes, etc. so as to encourage free agents to consider Dallas. And, hey, I've got no gripe with that; I think that it's his money to spend, and he can spend however the hell he wants. But it all rings a bit hollow when he's trying to play the "moral high ground" card, given that -- but for his lack of luck with the Lakers and Heat front offices -- he would willingly ignore the luxury tax to pay players. You didn't seem so worried about competitive imbalance when making all those facility improvements; THAT doesn't give you an advantage over, say, the Spurs and Grizzlies?
It's not that he doesn't make a point; I just don't think he should be the one making it.