Gore isn't the only reason that a game gets rated M in the US.
For example, Fable 2 is rated M in the US, but that's not because of gore or violence, but because it contains adult themes (e.g. sex, alcohol, homosexuality) and was actually rated suitable for 15 years olds in it's home country.
There are plenty of games on the 360 that aren't M rated and also some games that are M rated but don't contain a lot of gore and are considered suitable for younger people in other regions.
If you get a 360, you won't be forced to play only gory games and in fact, the games that get bundled with it are relatively gore-free and not M rated.
Forza 4 is a gore-free racing game deemed suitable for all, and Skyrim is another game that is suitable for 15 year olds in other regions but has earned a M rating because it has alcohol and sex references, the bloodshed in it is quite mild, the is gore conspicuous by it's absence and it's violence little more than breaking open a piņata.