WHS has its own disk spanning solution ....
....so all references mad in the article and other user's comment about this box not supporting RAID are kind of futile. You could not install WHS on a RAID system even if you wanted to, tried myself when I started off with WHS and quickly found out that WHS uses it's own solution for this. As an earlier 'anonymous coward' commented: "This device has a heterogeneous disk spanning, file replicating and redundant file system...".
Although for simple file sharing and services like FTP any potent NAS would do, the WHS solution gives you much more flexibility and access to a host of add-ons that can be useful in many other ways. Obviously, if you do not need/want this, only the superb back up solution should be enough to satisfy most users.
Agreeing with earlier posters the storage limit on this ASUS box can be an issue. It is relevant to mention that the WHS filesystem is able to add in external devices attached to the box (in this particular box this would mean using the USB (6) ports or E-Sata (2) ports). If I where buying this box I would probably be thinking about attaching a cheaper 2 TB drive using e-sata (consider the Samsung Story Station Plus 2TB which is around €150 euros in NL). It will integrate seamlessly into WHS and you'd still be able to expand after this.