I am going to an a la carte mode of a dj night.
From grand intros to last dance...everything is included in between for a rock bottom price. It's a take it or leave it. Even though I am priced higher than other djs in my area, and we have a lot of budget shoppers, it hasn't been hard to sell them the whole night as opposed to just 4 hours of dance music.
After explaining the benefits of using a buffet style service, they can see how much of a difference a better flow of the night can really be.
On to this subject...most of my weddings are in the 160-200 range. I don't think I have done a wedding with less than 100 people ever. I have done plenty bar gigs in which there has been some real low turn outs, but never a wedding. Likewise, I have done weddings up to 500 or so people. So really it varies.