I don't think it's as much a "speed cap" as it is that the management is trying to share ONE cable connection among all the apartments. Sure, a single cable connection can get you some pretty fast speeds, but if you're sharing it with a dozen or so of your closest friends, it gets bogged down.
With cable TV, you can split and amplify the signal, and everybody gets decent quality. NOT with cable Internet...
My take is that your apartment complex's management is trying to pull a fast one with their "free broadband" offer.