I don't like the auto-gratuity, but it makes sense. Large groups usually occupy their table for extended periods of time, and the server has to spend a lot of time at the table to take orders, get drinks, etc., diminishing their quality of service at all of their other tables. It makes sense for a restaurant to make sure that the server doesn't get completely screwed over by some bad person covering the check who only tips $2-3, regardless of what the total bill is.