You could write something like Cassandra or Lucene in Python. Python is a language (much like Java, BTW). You could then run it under Jython or PyPy. The GIL is unique do CPython, AFAIK.
And you are right - CPython is the canonical implementation of the language. The fact we can use a reference implementation in production environments is great.
You probably wouldn't be able to write something like Cassandra in Python 2.7 and expect it to run unmodified under Jython or IronPython, but you could write it in Python 2.5 and run it under both 2.7 CPython (with the expected multi-core annoyances) or under current Jython.
And you can't have painless C modules in Java either.
There is no such thing as "You wouldn't be able to do [cool-multi-core-product] in Python because of the GIL"