I think a proper cap would have a good and a bad side to it.
Even if it is world wide whats to stop Mr Abramovich buying some **** ant Aussie team (not a controling share obviously as thats illegal) and saying "you pay this guys wages and i'll donate this much money to your club everyweek and you loan him to me at Chelsea" Things like that would still be legal in the game. Any way you look at it money talks. Plus the less money players are making the more likely they are to rig a game or **** around outside the game doing promotions like Beckham.
Obviously if it did work, and ticket prices really did come down i'd love it, as at the moment they are ridiculous when you consider that its £50 in some places for 90 minuites of entertainment and your not even guarunteed entertainment. Supporting a club is one thing but throwing money at them so that they can pay a guy who doesnt really care about the club is another.
Plus when you look at it your not going to be talking about wage cuts, your going to be talking about players being released entirely so that the club can still feed the likes of Edgar Davids or Thiery Henry or Steven Gerrard, it wouldnt harm them, it would harm the club though as they cut the contract of breakthrough players and slash thier wages.
To be honest, the only way i see of stopping that from happening, is to make each team register a squad at the end of each transfer window (as with the UEFA competitions) and this is the squad that will have its wages capped. It will be hard on the reserve and fringe players but this way they get to carry on at the club rather than be forced into joining Millwall to make ends meet. It also means that the club can give Michael Owen his £105k a week and it wont affect some little sod in the reserves who they've never heard of too much as hes in a seperate wage bill altogether. Obviously it will still mean you'll see less teams full to burst with star players like the current Chelsea team, but it will mean that clubs will have to think long and hard about each transfer rather than spring for every player who comes available with a half decent rep.