I've known guys riding sport bikes reverse the tire and the only thing you don't want to do is ride in the rain. Said traction was no different.

 

Years back when I was selling bikes there was a time where some local riders found a specific model of Bridgestone knobby worked better backward than the proper direction of rotation for the terrain they rode.

There are only two reasons for a direction of rotation:
1) The way the tread sheds dirt, mud, or water (street), probably the most important for off roaders, but you only learn if it is by running the tire backward. 99-44/100% of the time it will have no effect, only at the extremes.
2) The direction the belt joint is laid up in the mold, not at all important to off roading, but probably extremely important to road racers, drag racers, or other extremely high speed high heat applications. I was told in a seminar that it really isn't an issue on street tires, but is still used to dictate the direction of rotation on symmetric tread tires. In addition I figure if flat trackers can go out and abuse the tires they use so hard, then flip them to run the other side the same way, this belt thing is of little importance and is another example of lawyers covering butts.

 

The motor cross tyre that I have is for soft ground in one direction and intermedite ground when reversed

 

Maybe the companies figured something out by riders running the tires backward...