I think they've nnswered this one before.
My understanding (fairly worthless as far as it goes, but it's somewhere near the truth) is that each release requires them to compile and distribute the code, which requires a non-trivial amount of work. In addition, their release cycle is not simply "Well, we got all this stuff done which we then released in 1.04", it's more along the lines of:
A. Develop New Stuff
B. Finish New Stuff
C. Release New Stuff in a new version
D. within 24 hours patch the really bad bugs
E. Within 72 hours patch the really annoying bugs
F. Within a week fix the other stuff.
G. Develop New Stuff.
In short, releasing a new version isn't a simple, fire-and-forget affair like something you'd pick up at the Alcoholic Divorcee Lounge on a Saturday night. It's a process in itself that takes several weeks. Doing that every time the art is ready and the flight model is close (think they have an arrestor hook yet?) just isn't efficient. On the other hand, if you wait too long between revs, you risk letting the game go stale.
By the way, they're not really invisible or silent. Your neighbors are lying to you.