I notice that Ducati still loves them, but why? To me they seem more complicated, needing more maintanence, therefore higher cost, to achieve the same thing that modern valve timing systems get with valve springs. If a honda motorcycle engine can spin up to 16-17k rpm with no valve float and making power, why does ducati insist on using desmo valves for engines that see, what 13k rpm max?

its their trade mark. I honestly think they keep using it because it was cool 20+ years ago. Metulurgy has come a long way, valve spring performance is drastically better than it used to be. There is no real need for it anymore.

At least they stopped using the bevel gear driven cams....

it's because they're much more expensive and people are willing to pay for something with a cool sounding valve system. if it works and people will pay more for it, why not use it?