My personal opinion is that this legal reason is a *huge* bottleneck against external contributions. In particular, because you need to deal with it *before* submitting any patch, which, given the complexity (4MLOC) and growth rate (+30% in two years) of GCC, means in practice that people won't even start looking seriously inside GCC before getting that legal paper.
Simply not true, you can submit patches without the legal leg work done. The patch cannot be commited to the tree though. And the time it takes to do this is less than it took me to read your message... Any even since I did send patches to GCC since several years, I am still scared even now when sending one. Sorry for spaming the list with such non-technical blabla. You should be more scared of that then sending patches. :-)