I thought Cheers was filmed before an audience?
"Cheers" was filmed before an audience, as are 99% of shows that have a "laugh track" -- but they all "sweeten" the audio to some extent; probably the two most common reasons are because they didn't get enough laughter from the audience, or because they need to "cover" an edit. ("Cheers" was probably more in the latter case.)
When I worked as a closed-captioner, we would usually get tapes of shows that were dubbed for us before the audio mix was fully completed. That meant, on most sitcoms with a laugh track, we got them before the audio was sweetened and we'd only be hearing what they'd recorded from the live audience. It changed many of those shows quite a bit -- they seemed less funny when there was less laughter.
At any rate, there are sitcoms with a laugh track in the UK as well. The one I've seen most recently is "The IT Crowd" (which I thought was funny enough that I could ignore the laugh track).
Edited by trainman, 19 September 2011 - 09:53 AM.
Edited to respond to paulman182's post