It is happening in Pr, but it is subtle. However, when put into Quicktime or H.264, you can really see it. It does transfer to DVD. You can tell the position and scale are moving across the still image and it kind of drags.
I seriously doubt it has to do with processing speed (see below).
My system:
Mac Pro
Quad Core Intel Xeon x 2 (8 Core)
2.4 GHZ
16GB RAM
WD 600GB HD 10,000rpm Raptor (OS, Apps and Project Files)
3 1TB WD HD 7200rpm in RAID 5 (video and audio assets)
1TB External G-RAID mini RAID 1 hooked up via eSata (exports and backups)