It's usually 1 game over others that gets me to buy a system. I see nothing wrong with it because I'll always get more games I find interesting. Sometime you need that one big push.
Got a Xbox for Halo: CE. 100% worth it.
Got a Gameboy color for Pokémon Gold
Got a Gameboy SP for Pokémon Emerald
Got a Xbox 360 for Halo 3
Got a Ps3 for Last of Us