I think that weight has alot to do with it. I changed my tires before my cross country trip (7200 miles) in May. I have had good luck with Pirelli Diablo Stratas so I put on a new set 500 miles before I left. I had to change out the rear, with about 8,000 miles, when I got home because I had been riding a plug for about 2000 miles and it had developed a serious flat spot in the center. The front is still going strong, with NO cupping, with about 10,500 miles on it. My normal time frame is 8-9k for both the front and rear, with the front usually have a good bit of cupping. This is the first front tire that I've had that did not have cupping after 6k.
I see the difference for the wear around town as opposed to a trip being that I was loaded much heavier in the rear for the CC trip. Around town I normally have the top case only and no side bags. The CC rear loaded weight seems to be the difference in allowing the front to go much further than normal.
My average wear is over 19k on my 04 and 34k on my 06, so it would seem to indicate what I should expect to get with my riding style.