OK. Another non-expert answer. But I read a lot. So bear with me.
Are the hi-perf struts shorter? Yes. Often the shaft is slightly shorter.
Why would they wear out? Well, think about a properly damped suspension. You hit a bump, and the damper goes through one jounce and rebound cycle. Now stiffen the springs. Now the damper goes through several jounce and rebound cycles before hauling in the energy absorbed by the spring and converting it to heat. Add to this that the damper is operating in an area of travel that it wasn't designed for, and... hmmm.
My theory is that your seals wear out faster, perhaps because of the extra cycles cause by almost continuous up-and-down motion.
But I'm not an expert.
