i wouldn't worry too much about it - variety is the spice of life as they say.
these days it's harder to fill clubs than it used to be, especially techno events. and people paying to go to clubs just want value for money so booking more artists makes sense when filling events, especially the bigger ones where more is at risk. and either way, it just depends on the night doesn't it? and who's on.
surgeon is playing in two hour set in leeds next week. nothing wrong with that. he played for three hours for us last and he was awesome, people loved it. but i still think that these days most would be just as happy to hear him for one hour if the dj/live act following on from him was just as good.
30 minutes is a bit ridiculous though. i agree with you on that.