Look at it like this: The Hemi has the longest pushrods and the largest rocker arms. The pushrods have to be quite beefy to withstand the sudden loads from valve opening. It probably uses a a pretty huge spring to control those behemoth valves. The piston in the hydraulic lifter has to withstand the accelerative forces of valve opening and closing. The more aggressive the cam lobe, the more the inertia loading that the hydraulic lifter sees. So is it going to leak down? pump up? oscillate?

The solid lifter has far less to go wrong and is probably lighter to boot.

R.