You should go read up some on past iMacs launches. Check the archive on this site. It's been many years since last time they had stage time. It's usually only with complete redesigns. It might be redesigned Tuesday, but it might just as we'll be a silent launch on the homepage like usual. I'm with 42 on this one. Probably 60/40.
Actually, just the fact that they don't advertise the iMacs should tell you at it often won't get stage time.
I can't remember the last time I saw an iMac commercial. Years?