MLB has a "soft cap" when it comes to team salaries. Not sure about the NBA, but there seems to be some flexibility there, too. The NFL has a hard cap. The way to build and maintain your roster is entirely ruled by the tyranny of The Cap. Jerry Jones throws too much money at too few players. That's his M.O. And the Cowboys lack depth year in and year out.
The NBA has a soft cap. The MLB has no cap at all, but they impose a luxury tax.