Wire_Mark:
1) For your information an aircraft turning back does not mean that the problem is serious enough to divert to the nearest airport. I was on a KLM flight which developed a problem 2.5 hrs into my flight to YVR. We went all the way back to AMS.
2) If it was an engine issue, it may well have been shut down as a precaution and not actually "failed". The a/c is perfectly capable of flying on one dong and it makes economic and logistical sense to return to the company's maintenance base if all else looks good.