Quote from SenturaHalf-life: Source was bullshit, they're fixing it!
that's a feeble excuse.
No one needs an excuse to mod. You're not in it for the "glory" or the (non-existent) pay-check. You do it because you want to do it and you enjoy doing it. That's it. For the love of the game, art for art's sake, design for design's sake, etc.
That said, I think we should all follow the Adam Foster model: Periodic, self-contained, highly polished releases until Valve offers you a job.