The difference is (at least partly) due to the difference in valve adjustment method. The air/oil cooled Bandits use a screw & locknut adjustment in the rocker arms whereas the Yamahas with 26K intervals use shim under bucket on the valves. While the screw method requires more frequency, it is quick and easy for even the most neophyte mechanic to perform. Shim under bucket method requires camshaft removal to adjust as well as an assorment of shims. On the bright side for the Bandit is the valves don't usually move much, if at all, after ~15K miles. Personally, I check mine annualy and I put ~10K miles/year on mine and haven't had to make a physical adjustment since my 15K check.
I do believe the new 650/1250 water-cooled Bandits use a shim under bucket system and have long intervals, too.