[king_jester]

Its not a hard cap, its a cap of number of residencies that will be supported by federal funding through Medicare:

http://www.advisory.com/daily-briefing/2012/08/30/why-reside...

A large majority of residencies are funded this way due to the very high cost of residency. As a result, many private institutions won't increase residency numbers on their own due to funding.

The main issue is the cost of residency is massive and is prohibitive for private money to fund anyone's residency.