To each their own!!
http://www.edmunds.com/car-care/stop...-your-oil.html
FULL SYNTHETIC can easily go 7,500-10,000 miles, of course depending upon driving habits, roads, environments, etc.
Some folks change oil and filter when the oil is reminiscent of Tar.
Some never change oil and filter because of some misguided belief in "No Maintenance" for up to 100,000 miles.
(these are the same folks seen on sides of roads or parked in travel lanes with flat tires, open hoods, smoking engines, etc.)
FORD suggests using 5W-30, too bad, I'm going to 10W-30 Full Syn and a Wix or Purolator Filter at next change up.
It's YOUR VEHICLE, do as thou wilt.
CHEERS!!