keep in mind that SEGA, signed a contract with the creators of Wonder Boy series ( as they did with most of the game companies, which put them in the red ), and the deal pretty much said "all names, titles, and etc belong to them, but the world was shared. This is why when they wented with Hudson Soft ( which was the better move ), they had differnt names, and appearances.
Sega is basically using their license ( and property rights ) of the games to release these games ( as downloadable content ). The same could be said for any other current hard copy releases.
I own most of these games, and the actually hardware. So why would I need these games. Portability is not an answer.