Is the 21.5" an IPS display? It is sorta disappointing that Apple got rid of the "perfect" for me sized 24" iMac. I have a 24" LED ACD, that I connect to my MBA, but I was really close to getting a 24" LED iMac when it was released today... too bad the 24" didn't happen although LED and larger iMacs happened. I also don't know about going 16:9. I really liked how Macs always had 16:10. It seems obvious that Apple is preparing to CAVE on BluRay. I suspect Apple decided to wait to include BluRay in all Macs at the same time when the MBP/Mac Pro are updated next. It just seems like Apple needs to wait until it can offer BluRay in ALL Macs. I suspect a March 2010 Arrandale update with BluRay appearing in all Macs.
Both are IPS. Probably E-IPS rather than the existing H-IPS, so lower quality, but probably nothing to be concerned about.