Not unheard of on any engine, but not common either. Definitely not a warranty issue, that's for sure. Either you use bad gas, or you have other maintenence issues that have contributed to buildup (EGR valve, PCV valve, etc.)
You can clean the throttle body yourself, just get some 02-sensor-safe intake cleaner, disconnect the rubber tube ahead of the throttle plate, open the throttle manually (engine not running) and spray it down (don't spray too much) and let it sit a while. Start the engine, spray a few more short bursts while you manually operate the throttle (blip it, don't try to rev it much over idle) and then shut it down and put the intake hose back on.
Brent