This massive ommission in MobileMe isn't a big deal to me for calendars related to holidays, sports schedules, movie releases — full list at Apple's calendar page — but it's a huge deal if you subscribe to calendars published to the Internet from someone else using iCal. Especially for families or businesses that maintain and share several iCal calendars.
So you can sync read-only calendars to your iPhone with iTunes syncing, but with MobileMe you're out of luck.