That is true. But Lauren Sansonetti has really done a lot of work: he is the main developer and every now and then he would merge his own branch which is full of the kind of features and improvement that take a while to develop and cannot be merged easily until a late stage.

So I would say that Apple is by far the main developer of MacRuby.

That said you are right that one full-time developer doesn't look like much of a commitment from Apple. And I think that was the case. My feelings (and of course these are very subjective) was that Apple supported MacRuby partially as a way to help Ruby on Mac and partially as a research experiment.

I hope at some point Apple decides to really put its fiches on Ruby: that would be awesome. But MacRuby on iOS is very much the kind of thing Samsonetti loves, so I wouldn't be surprised if it's all his doing, and nobody else's within Apple.

One last note: Apple also supports LLVM on top of which MacRuby is based... so not sure how many people that would correspond to in your: commitment ~ sponsored people equation. :)