Satoshi Nakamoto released Bitcoin SHA-256 under the MIT/X11 Open Source license for the specific purpose of allowing the creation of other versions of Bitcoin (aka Alt-coins).
The opposite is true, in fact. He released it under the MIT license so that people wouldn't feel the need to rewrite the main Bitcoin client:
If the only library is closed source, then there's a project to make an open source one.
If the only library is GPL, then there's a project to make a non-GPL one.
If the best library is MIT, Boost, new-BSD or public domain, then we can stop re-writing it.
I don't question that GPL is a good license for operating systems, especially since non-GPL code is allowed to interface with the OS. For smaller projects, I think the fear of a closed-source takeover is overdone.