The TE570 was thoroughly revamped for '01, with a new frame, new bodywork and ergos, and numerous internal engine mods. I think it won the open class in World Enduro last year, maybe the last two years. If you take a look at the design of the engine it's actually very similar to the CRF450 Honda--4-valve SOHC with a forked rocker arm and automatic compression release, except the TE570's engine design in various iterations has been around for a while and is basically bulletproof.
Husky's new 250/450 4T's are all clean-sheet, all-new-from-the-ground-up models for '02. They use an all new DOHC e-start engine with a pretty cool F1-style valvetrain and Ti valves.