Three years ago I wrote an entry here about my feelings on buying the exact same game for more than one console. Since that time I've slightly, and I do my slightly, laxed my opinions on that matter. For example, I would love to get 18 Wheeler for the Gamecube, simply because I love the Gamecube, even though I already have it for the Dreamcast and it's the exact same game.
But sometimes companies will release a game and add slightly varying content for each console, such as the Mega Man Anniversary Collection for the Gamecube, PS2 and Xbox, so I would gladly own them all. Or perhaps a company will release a game on one console, see how great it's selling and then release it with a slightly different title for other consoles, such as the Sonic Mega Collection and Sonic Mega Collection Plus.
Sonic Mega Collection was originally was released only for the Nintendo Gamecube, until things got a little greedy and they decided to release it as Sonic Mega Collection Plus for the PS2 and Xbox. Sonic Mega Collection Plus added additional games to the roster, including most of the Sonic games for the Game Gear, making it completely unfair to the owners of the Gamecube version. The Gamecube never saw a release of Sonic Mega Collection Plus, but the score was upped by the (in the USA) Gamecube only release of Sonic Gems Collection!
Without a Sonic Mega Collection Plus for the Gamecube, my only option was to hunt down a copy for either the PS2 or Xbox. Which just so happened today, at the Goodwill 50% off sale! The original price tag was $5.99, so I only paid $3 for it, so I can't complain. For what I paid, coupled with the additional games and the overall fact that it's genuinely a great product, I don't mind owning this and the Sega Mega Collection for the Gamecube, although I doubt I'll be playing the Gamecube version much from now on, rather I'll be hunting down a Sonic Gems Collection.
That brings me to the fact that I do own most of the Genesis Sonic games in cartridge form, so why would I want to own them again for the PS2? Well I guess it's ease of use. It's easier to pop in a disc to my PS2 and play games I don't own (the Game Gear Sonic games) alongside the games that I do already own. I mean, they're all on the same disc, so why not?