Here is a good article about how cars determine the oil life and when to set the light. it also talks about re-setting the monitor and gives some interesting history on the subject as well. From the article:
"The most important thing to remember is that these estimates on the health of the oil are built around specific oils recommended by the automakers. Since the vehicle has no idea about the specification of the oil, it is critical the oil matches the oil life monitor..."
There is also information about Longer-Interval Oil Filters. From the article:
"You can’t judge an oil filter just by opening it up and counting the pleats. Most reputable oil filter manufacturers have a warranty that will cover engine damage if the filter fails within the OE-recommended oil change intervals. If a filter manufacturer does not have this type of warranty, don’t take a chance on their filters..."