The chances that the UFC fixes fights is pretty slim, for the reasons you stated above. And nothing about last night's fights screamed "fix" to me.
But it would be naive to think that fights don't get fixed from time to time one way or the other in the UFC.
All sports have an element of match fixing in them. The NBA had a huge ref scandal not that long ago that's been swept under the carpet, FIFA had its thing a few years back, turns out that upwards of half of the Emperor's Cup Sumo matches were works, and Bob Arum's Top Rank boxing has been raided by the FBI numerous times (evidence is pretty overwhelming that Butterbean was pretty much just a pro-wresting style sideshow working over journeymen being paid to take it on the chin).
People who believe a sport with as many moving parts, uncertainties, salary disparities, and gambling links as MMA has doesn't have fixed fights are really living in denial.