[devnill]

Yes and no. You will get slipping on heavily worn cassette (read: sawtooth shaped teeth) and a new chain or vice versa, but heavily worn these days might be 4-6000 miles of abusive riding. For the average commuter, this would be several years of use, as well as a fair deal of casual riding.

[elif]

I stand corrected. I've never had that happen before but i'll take your word for it.

I still wouldn't consider a cassette something you should change as a matter of regular maintenance. Certainly not as often as a chain. I've had cassettes last through multiple wheelsets.