Once you've handled one (i have) you'd realize that there is a VAST difference. The HK pistol pictured uses a stamped sheet metal slide with a roller locking system similar to that of the company's G3 automatic rifle. The slide itself is only about 1/16" thick stampings that attach to a seperate breechblock that actually closes the chamber.
The HP slide is a casting held closed by inertia and the recoil spring.
The similarities cosmetically are striking but just cosmetic.