HP's MediaSmart software adds quite a bit of value (I'd say about $100 worth) to the Windows WHS OS. Mac support, Itunes support, a support network,... HP smooths the rough edges on WHS. (How do you install WHS on your system without a DVD? HP has a uPnP installer that runs from the DVD on any Windows system in your subnet.)
The MediaSmart box is really small, good looking, quiet, low-power, but more than powerful enough. It's also "Drobo-like" in that you only need to look at the lights - if they're all blue, she's happy. See a purple light, take a note to check into it. See a red light, open the console now and find out what's wrong.
I've done a lot of DIY systems, but the HP system is nearly perfect. The only shortfall for me is limit of 6 TB internal storage, but if I need more I'll hook up an eSATA RAID box.
By the way, if any of you have the EX470/EX475 and haven't upgraded the RAM to 2 GiB - do it right away. It makes a huge difference, and it's very cheap to get a 2 GiB DIMM these days.
And, did you realize that your Newegg FrankinWindowsHomeServer is 3.7 times bigger than the HP box, and probably uses a lot more electricity!