depends on the promoter & the DJ's ability to fill the "slot"
I like to see a DnB DJ that can roll 25 tunes in an hour, and keep shit interesting. As far as a techno dj goes, there music is much more boring, i would expect to see them play 30-50 tunes in an hour.
As a promoter, you dont want to have too many people playing the show. You dont want to pay everyone. And you want the headliner to have a showcase slot, (who wants to see the promoter play for 3 hours and the headliner for 1 hour?)
all that stuff is really relative. Its a matter of what you like, and you should support it accordingly.