"but if it hadn't been for gplv3 do you really maintain that apple wouldn't have stuck with it as a frontend for longer? "

Yes. Absolutely. It's been mentioned numerous times at conferences and other in-person meetings.

Apple did not write clang because of GPLv3. They wrote clang because they needed something that was

1. Faster than GCC 2. Offered better diagnostics 3. Could offer code completion and indexing for XCode.