Well, it's cheaper than having a course built with an accurately measured length!

But considering that lots of people already have GPSs for hiking or portable units in their cars, in their phones, or you could borrow the Garmin 305 from the cyclist next to you for a mile, and it'll give you more accurate results than pretty much anything else (though most of the methods given are already plenty accurate), it was worth mentioning, in spite of your "thats huh....expensive" claim.