I've heard this again and again, and yet every time I see open source used by a company, there are patches being applied, compliance concerns and audits, and integration efforts.

Sometimes this effort costs less than writing the code yourself (such as integrating with a database), but not always.

Apple and Microsoft, for example, have taken significantly from BSD/Apache-like code for their own OSes.

They wouldn't have been able to do that with GPL-like code.

Apple at least has contributed a lot back - they are a major force behind clang for example.

Then explain Android.

an android phone is oss android plus a bunch of proprietary (non oss) google bits.