Well i think 98% of hiphopcats misinterpret what mastering implies and what's BENEFICIAL to be able to really master anything. ergo, wishful thinking lol. "owning" mastering plugins is probably the least demand for being able to do a mastering. Im not saying you need hardware to be able to master as currently its pretty much hybrid, but it will cost you in the least a 10K. If you'd master itb and have a good room then you'd still spend 5k on speakers (aside from room treatment). Proper ears and a proper setup makes you HEAR the difference between using cables, aside from the rest of the chain. If you cant hear such a difference, seriously...leave it alone.
You dont master anything for internet, you render an mp3 from a master. You do master for various media indeed, but this is regarding the limitations of the carrier. Vinyl for example needs different mastering since it susceptible to wide stereofields and bassheavy tracks. By this it doesnt make the track sound better but prepares a fail proof master for duplication. Mastering in this case implies keeping the dynamics of the track and keeping frequency ranges as much as possible.
Mastering for cd/dvd is the same as for broadcasting, since broadcasting uses heavy limiting already there is no need to treat it differently.
Anyway, in short, i consider these mastering's done by the 98% of homeproducers a gimmick to fix up a crappy mix, adding just more compression and brickwall limiting to gain the phatness...also refered to as the loudness war... imo in all those cases, work on your mixing skills and check up with a decent mastering studio.