Well the sheer volume got annoying. But I don't really mind the reminders. My average mileage per year is slightly below the norm, which means I start getting the reminders when I'm quite a few miles away from 15000. They say...or every 6 months....but I'd rather wait until I hit the mileage mark. The biggest thing was that the 15000 mile service is basically just a tire rotation, and they "supposedly" inspect things. IMO it's barely needed. I'm always suspicious of how thorough any "inspection" of the vehicle actually is, and the tires I believe could of gone to 20,000 with little impact either way.
Yes, it is common practice, and it's not new. Often I receive cards in the mail asking me to sell my car back to the dealer. It's just a sales tactic to get you to buy a new car because the dealer knows that if you sell your car you will need a new one, and you would likely buy it from them. So they give you a good deal on the sell back but a bad deal on the new purchase. Just more money from them. This is not new.