Some race on sims just because real racing is waaaay too expensive for some. For professional karting, I would have to spend at least 2x my monthly income just for karting in order to be competitive. So it's completely out of question for me.
While I do agree that some things don't need to go extreme in LFS, I think that warming up the tyres are part of the hotlapping, and it puts some restrictions for the setups (since the driver would have to take care about overheating the tyres). And somehow I think that it could be an option to start from the pits, since some purists will like this option (except on AS GT with UF1.... )