First off, comparing front and rear wear on a bike is different because the vast majority run differnet size tires. Secondly, you have different model and brands of tires front and rear. Depends how you dide a lot too. More cornering will wear the front faster, more long straight driving will wear the rear faster. From several years of reading on several bike forums very rarely do front and rear tires wear at the same rate and in the same way. I have my miles divided between too many bikes to have needed tires so I can't say from experience though.
good article on it
Motorcycle Tire Wear