Usually that's new features and bug fixes. It's very rare to find a client who'll happily pay for refactoring. If you're in a job where you get time for that you should consider yourself very lucky indeed.

EDIT: For what it's worth, I agree with your point about code quality. What's 'beautiful' now is only 'perfect' in the frame of the current feature set. It might be horrible if the next feature that comes along changes things dramatically. I'm very much of the opinion that "good is better than perfect", just with the addendum that the code at least has to be good. Bad code is just bad.