Our reasons for having a proprietary version is clear. We want to build the best graph database out there, and having money helps us do that. Our free version contains all the features that would be needed by a startup to run and scale their operations. The presence of proprietary features doesn’t make something crippleware. If we removed features, then yes, but we didn’t do that. So, I won’t expand or defend that any further.
But, just to guide you, if you’re looking for a graph DB where there’s no commercial interest by any particular company, or the developers of the software, you should look at http://janusgraph.org/. It’s a fork of TitanDB.