In the first few (maybe twenty? I'm not sure) games your elo changes are much higher than afterwards. That is to let new players have their 'right' elo a bit faster, whereas players with a lot games have kind of 'proved' their current elo so that the change needed for their elo to become 'right' is smaller.
Of course one shouldn't put that much emphasis on the elo value in a game that relies quite heavily on luck, like for example saboteur - just play for the fun of it. Elo had been created for chess and on this site it is adapted to other games as well. Thus it isn't perfect but I for one don't know of any other rating system that is perfect.
