Well, it's about bypassing App Review and other static security analysis, undocumented apis, etc. I think there's a fairly strong case here that it's about more than just protecting revenue (which it is also!)
Given the sandboxing and the security architecture of iOS, my conjecture is that apps could be perfectly safe even in light of the use of undocumented APIs (calls to which can be and are obfuscated even in today's setup) and accidental security flaws (which can and still do exist even in today's setup).