As people pointed out, Pope Benedict is 80 years old. And he’s already traveled to Germany twice, Poland, Spain, and Turkey. In a couple weeks he leaves for Brazil, and is potentially putting a visit to the U.S. on the calendar at the end of the year.
If you compare him to the amount JP2 traveled when he was 80, I’d say they’re right around on par. You can’t expect an 80 year old to compare to a pope’s actions when he was 56.
Also as was mentioned, in midst of JP2’s globetrotting, the Vatican got in a bit of disarray. It seems Pope Benedict is following the biblical advice of “Noticing the log in your own eye” before going to to fix someone else’s.