The new storage options probably have wider appeal. The Pro comes with four drive bays, each of which can now be ordered with a 2TB drive, up from the 1TB options available before. These drives aren't cheap, either -- Apple wants $550 for each one installed to order, a good $200-300 more than you can buy a bare 2TB drive for yourself. They're high-quality drives, though -- 7200 RPM, 3Gb/s, faster than many of the cheaper options -- and would be supported by Apple.
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The Xserve also can be ordered with the 2TB drive in each of its three drive bays, for the same upgrade price. Moreover, the server is now available with 4GB RAM chips -- up from the previous two -- meaning that the single-chip Quad-Core model can now handle 24 GB, and the dual-chip model 48 GB. Each 4GB chip costs $450 installed; I see them for $160 to $370 elsewhere, so it's hard to say how overpriced that might be.
Also, the notes on the Xserve say it will support up to 96 GB of memory when used with Mac OS X Server 10.6 (Snow Leopard Server). That means it must work with 8GB chips, even though Apple doesn't yet sell those. (Nor do any of the other sources I've checked.)