I think you're missing something. What they were doing before was Linux only hardware built on non-Apple PPC motherboards.
This hardware runs OS X. It's built by Apple!
At first I thought they must just be buying off-the-shelf Apple hardware and sticking the guts into thr rackmount cases, but a close inspection of the specs reveals that's not the case.
They come with only 1 PCI slot and it's a 64/66 slot unlike the 64/33 PCI slots that come with the PowerMacs. They also only come with 2 DIMM slots, not 3.
This means they have an agreement with Apple where Apple builds special rack-mount PowerMac internals for them. I think that's one interesting bit of news that relates to Apple's future hardware plans.
Read the FAQ. It states that this is an Apple motherboard, the same that comes with the Power Mac. It comes with a right angle PCI adapter that covers up the other PCI slots. As for the RAM, all they are saying is that it comes with 1GB RAM in 2 modules, but that does not mean the 3rd slot is not there.