It's not riding fixed that stresses the bearings but I'm fairly certain that riding fast and suddenly locking up the bearings to skid (as most fixed riders do) would put added stress on the way the cartridges fit into the cups in a way that wouldn't occur during normal riding and not necessarily the bearings themselves. I know people who have blown through Sram GXP BBs in under a month on fixed gear bikes ridden on the street (not track bikes) while others who use them on road or mountain bikes have had them for considerably longer.

At any rate, I don't have the trouble you describe with over-torquing or under-torquing my square-taper cranks because I majored in rocket science.