Wide bars give better control over rough terrain. If cyclocross racers were released from UCI rules, the bikes would probably look a lot like XCO hardtails. What makes the sport in many ways is the "wrongness" of the bikes.

In the cat 4/5 singlespeed groups I race in, there are flat/riser bar bikes. In fact, quite a few ppl just ride SS mountain bikes with 2"+ tires. There's no one checking tires will a caliper in the novice ranks.

I do like the spirit of the "fixed or slicks" rule in tracklocross: if you don't want to ride fixed, then you need to ride 23/25mm road slicks. If you do ride fixed, then fat and knobby are allowed.

I have been looking for a midwest tracklocross race to try. Maybe next year!