Agreed. I also wish that Apple would incorporate the professional graphic cards line (ati firepro and nvidia quadro) into the customisation options.
On the CPU front however, Intel hasn't released many new Xeon CPUs other than bumps in the Ghz area. This is probably why there hasn't been a need to update the MacPro line.
I do 3d rendering work and have a dual Xeon hex
Core workstation (24 rendering threads if u include hyper threading) from dell which was bought this year...