The boots tend to be on cheaper forks, and from past experience with a pair of Rock Shox Judy Cs (1999) the rubber wears out pretty quick (it goes baggy where it should fit snug) and crud starts to get into the fork internals anyway. Once this happens there's nothing to be lost by just cutting the rubber away and servicing the fork on regular intervals. I replaced my Rock Shox after a year, but the rubber was wrecked before then anyway.