The dura-ace top pulley has an extremely sophisticated pair of tiny ball bearing retainers that allow it to float on a straight spindle, and sealed with very much reduced diameter seals which entail much lower seal friction.

The rubber seals on Ultegra and XT top pullies traditionally have been very easy to get the lip pinched under the dust shield at some hidden spot, which further increases friction and quickly chews off the offending segment of the seal lip. Very easy to do while re-installing the pully with the chain getting in the way!

I apply light oil to my XT derailer's top pulley seals before each race, which helps quite a bit but is temporary.