1) People don't buy a top end MBP strictly for gaming. They may be willing to spend more for it to have a better CPU/GPU in order to game, but they usually would have bought a Mac anyway.
If gaming is the reason they get a 15" MBP instead of a 13", they're really just paying the difference (~$500).
2) You can't compare a 360/PS3 to a 15" MBP in terms of performance. Try a PS4/Xbox 3. The MBP will allow you to max any game at 1080p, while the consoles will give you the equivalent of Medium graphics at 720p with no AA. Also, you don't have to pay for Xbox Live gold to get online multiplayer and games are usually cheaper and more customizable.
If gaming is the reason they get a 15" MBP instead of a 13", they're really just paying the difference (~$500).
2) You can't compare a 360/PS3 to a 15" MBP in terms of performance. Try a PS4/Xbox 3. The MBP will allow you to max any game at 1080p, while the consoles will give you the equivalent of Medium graphics at 720p with no AA. Also, you don't have to pay for Xbox Live gold to get online multiplayer and games are usually cheaper and more customizable.