It's inconvenient and most people will pay to utilize the full extent of their services because of that so Apple doesn't really care. Overall, the potential loss of people from doing something like that is fairly minimal - plus, if they are doing that, they are improving their skills within the Apple ecosystem which could turn them to potential legitimate iOS developers in the future - really the entire program's purpose.
At 20 devices, that is already a chore. It's one thing to wait a few days through the App Store for everything to silently and wirelessly be pushed to devices, but its another to have to gather all devices, register them, build them, and repeat whenever you fix a bug or scramble when you find something potentially big wrong.
Really, the issue is the abuse that we've seen from people reverse engineering the protocols Xcode uses to register for the certificates (and in combination with other reverse engineered exploits to understand and take advantage of Apple's services). They're attempting to (and have) create automated tools to register Apple IDs, Dev Accounts, and exploit that to sign illegitimate applications that are warezy or stolen. That is the bigger issue out of this, not a petty person trying to save $100-200 (which is a limited and acceptable loss).
