Lonely Planet is unique in that it basically tries to give some level of coverage everywhere, even places that might only get a few thousand TOTAL visitors a year. Most other lines will only put out books for where there's enough demand and interest to make a profit. So there's a lot of competitive pressure to frequently update books for the hottest destinations.

I use Lonely Planets a lot, but the degree I lean on them can really vary. The more "foreign" the country (language, level of development, level of tourism-oriented infrastructure), the more it gets leaned on, and I also tend to lean on it in places with costs that are very hostile to budget travel (e.g. many places in the South Pacific, where only a small fraction of total services available will be affordable).