Slimserver/Squeezebox does gapless all the time. And i've read at least 2 or 3 people now asking for an option NOT to do it. Can't please everyone.

The Gapless option in iTunes is also there to prevent it from cross-fading a gapless album. Considering how few albums are gapless, a manul option like this isn't such a bad thing. LAME can also set a gapless tag which some software should pick up (not sure if iTunes picks this up). iTunes also does some gapless analysis, but I have no idea what it's actually checking.