umm, just to play devils advocate, lifts are hydraulic ...
for me it isn't so much the hydraulic jack that makes me not work under a vehicle supported by them, it is more the instability of them. jack stands save lives and limbs.
Yeah lifts are hydraulic, but every one I've used has mechanical locks that you set, then place the weight of the vehicle on once it's raised. Isn't it illegal to sell something like that without an included mechanical safety lock, anyway?