Sandman
It does, and it's not the same plugins, they are all different actual binaries (that sometimes, in turn, launch the same external binary).

I.e. the plugin *file* installed into the applications are not the same. You can't take a Photoshop plugin file and put it in the PSP plugin directory and it will work. Tony once thought so (as did Savageduck) with regards to Lightroom, but after some research it turned out not to be true.

nospam
some non-adobe apps pretend to be photoshop so they can claim to run actual photoshop plug-ins (same binary), usually not very well because they do an incomplete job of pretending to be photoshop.