I thought there was a discussion in one of the forums about this and someone claimed that not all DVR's record commercials. I don't recall which ones and maybe he was talking out of turn. If they all do it then I stand corrected. I didn't bother with DVR when I was with Time Warner.
Remember when Tivo first came out back in '99 and it had the capability of skipping commercials? That was quickly halted because advertisers screamed bloody murder. Ever since, DVR's record commercials and the only recourse is that 30 second skip button!