edit: I just noticed you did acknowledge the small user base. So, that being the case, are you actually arguing that some executive at Netlifx is like, "Nah - screw open source - we totally have the spare resources to develop a Linux client that will have a negligible return on investment, but they can suck it?" If it's not worth it, they won't do it. It's like accusing Linus Torvalds of not being open because he hasn't yet supported your feature-of-choice from some other OS.
Here's another analogy : It's like Microsoft Studios talking about how the development team used a Linux based compile farm and testbed for their new game but nevertheless, the game itself won't run on Linux.
For the record, I was a netflix subscriber and canceled a long time ago because of inaccessibility of their instant video service--If it won't run on xbmc, I'm better off getting it somewhere else like amazon Prime. I even told them as much. I still appreciate them releasing all of this stuff though.
They don't "owe" anyone anything. It's a for-profit company, and they're being generous with their infrastructure source.