I just had my check engine light come on and thought something similar; that it auto-illumunated when I hit 50K miles. The code equated to a lean mixture or something; turned out to be a bad vacuum hose. Luckily, the mechanic was honest and didn't try to talk me into replacing the O2 sensors or MAF.
I did call the Ford dealer and asked if the light comes on automatically at certain mileage intervals, but they wouldn't answer the question; just kept stating I need to bring it in to get it checked.
BTW, I used an independant mechanic. I don't trust my local Ford service shop; (Kelley in Melbourne, FL) they've burned me on a replacement key before. I called and asked for an estimate, was quoted $75, when I got there, the price jumped to $150.