It looks like Apple has silently added a hardware RAID option for the Xserve and Mac Pro. They are not the same card but share the same price, $999 ($899 education). The card for the Xserve replaces the built-in SATA/SAS controller so it does not use a PCI Express slot. The Mac Pro card uses the top PCI Express slot (slot 4) and connects to all 4 drive bays. Both cards support RAID levels 0, 1, 5, 0+1 and enhanced JBOD. Both cards also have a 256MB cache and integrated 72-hour cache battery. If I remember correctly, the RAID card battery (and maybe the cache?) for the G5 Xserve was optional which explains the higher price tag on these new cards.
So far, it doesn’t look like they sell the RAID cards separately for existing Xserve’s/Mac Pro’s. Luckily for me, we will be purchasing an Xserve in the next couple months so I’m glad this came out when it did.