Check Engine Light

I have a 99 Silverado with the 5.3L. I've been running about a month with the message center light that says "change engine oil." The other day, my check engine light came on so I was thinking I'd better get to autozone to have the code read. I wasn't in much of a hurry cause I was thinking one of the O2's finally gave up with 155k miles. Well, I got the oil changed and when I reset the message center light, my check engine light cleared. So, does this model truck let you run with a certain number of key cycles and then set a code? I really didn't think that the check engine light had anything to do with changing the oil, but it just had to be.