Why are Las Vegas cabbies so weird about tips?

[PITTM]

my favorite restaurant in santa cruz just switched from a traditional restaurant tipping scheme to a built in, mandatory 15% service charge. This sucks for many reasons:
a) they assume they will get no tip and perform as such.
b) getting takeout sucks because you pay 15% for them to put some food in a bag for you and then they look at you disapprovingly when you dont give them MORE tip.
c) Other customers have realized this and attendance has plummetted and the food now seems to be getting more expensive.
d) when i get awesome service, i will regularly tip 20-30%, in the 5 times ive been there since their new scheme, i have gotten awesome service 0 times.

i know, from this it sounds like there is no reason to go there. But they have the best food of any chinese place i have ever been to and its not close. I think the tipping decision was made because its a fairly expensive(13-20 buck an entree for chinese) restaurant near a college campus. I get the feeling lots of college kids were thinking "ill splurge a little and go to o'mei....oh sick, the bill is 70 bucks for 2 of us, we cant afford to tip. consider yourself stiffed".

so yeah, long ranty post. Moral of the story: tips are good because they make for better service. mandatory tips are bad because they demand mediocre service.