Sure the pressure for good working atomic commits is high when you can have working bisection in a DVCS. This is a good thing.
However I've often noticed with central VCS systems the pressure to commit before your set of disparate changes become too extensive.
Using a DVCS can alleviate that pressure by allowing you to develop locally with multiple small commits. Once you've fixed your regressions you can re-base into nice tidy commits, re-test and then push to the public repository.
AIUI Gnash is already using Bazaar so it really should be possible to have a clean commit history without breaking stuff on the way.