Your customers require perfection? You've got tough customers, then. I assume they refuse to pay maintenance/support fees on principle...

I don't think they're tough. They just treat IT like anything else they spend their money on.

To them, maintenance/support is for changes they want, not for fixing bugs that should have never been there in the first place. Less than 5% is for that.

Wow. I can't think of anything I've spent my money on recently that has been perfect, software or otherwise.