If we're arguing the difficulty of creating a feature-packed ITX board (note that this tiny thing has more embedded already than an SE or XE) ... note that the MegArray has probably *bought* them a square centimeter or more on the board surface, when you account for the passive components that have to ride around the CPU.
Not to mention that interchangeable CPUs are nice to have in general. (Beyond the obvious, a 'junk-bin' economy lowers the cost of upgrading and makes the price/performance a little more palatable; G3-XE owners can take the opportunity for a G4 on their mini and swap CPUs around; Eyetech probably doesn't make that much per-CPU and seems to have a hell of a time sourcing, so maybe a deal with a third-party* supporting the larger Mac market could benefit everyone and put the focus back towards board design...)
*Something along the lines of
AMD's authorized distributors; in this case, the 'slocketing' aspect adds a twist that makes letting someone else worry about it seem more attractive. Of course, if a company was ready to step in and fill that role more affordably than Eyetech/partners have managed themselves, you'd think they would've by now. (The more buying power Eyetech has, the less useful such an aggregator would be.) This also assumes that Eyetech's modules *are* rolling off the same lines as the boards, and this hasn't happened already...