Whenever I add a new video on Youtube, seconds later I always get a comment from some dime a dozen 'music' channel saying my 'content is awesome' and telling me they have free music to use on their channel.
I have no idea what these spammers get out of this, but screw them anyway.
EDIT: My thought on the message you received, Tuomo, is that any response will either get "If I could only get a Steam Key, I'm just getting off the ground... It will help promote your game" or "Well, for a nominal fee I can do a LP of your game that will guarantee xxx people looking at your game"