Have you ever worked on one?
I love my G5s, but the Mac Pros are a relative dream. There a WHOLE lot to like about them, and a whole lot of free space thanks to the lack of massive G5 heatsinks and a PSU that took up the entire bottom of the case.
On the 1,1-3,1, you can pull the RAM risers out and put RAM in without skinning your knuckles or flipping the computer over. On the 4,1/5,1, you can pull the entire processor tray out by undoing two latches. On all the generations, you have four HDDs that are right in front of you and don't require contortion or remember to insert them in the correct order as on the G5s. There are other nice little touches like a double height slot for the GPU so you don't have to lose an expansion slot if you have a double height GPU.
I work on the insides of MPs more often these days, and I always feel like going to a G5 is a step backwards.