Regardless of what is said about the ISP system (edit: from the manufacturers, I mean), I haven't seen what the 'perks' of the system are meant to be, but I'm guessing weight and stiffness? I've never had my saddle feel flexy. And bikes are made heavier (to meet weight limits) from the pro's perspective, so they wouldn't care for the weight, too much... Right?

From my perspective, it just makes the resale aspect of the bike near impossible, the next guy must have the same or lower saddle height than you.