You need to remember that there are a lot of people out there that are just ignorant of how to maintain things. Just because oil may go 10k or more miles doesn't mean someone shouldn't be checking level monthly and or replacing it sooner than 10k. Just because coolant may be able to go 100k miles doesn't mean one shouldn't check pH every year or so. Just because plugs may be able to go 100k or more, doesn't mean gap shouldn't be checked every 30-50k. By the time you do checks/maintenance, you may as well consider alternatives, especially if you diy, as you can save money and replace parts or stuff that is wearing out over time. The whole idea is to do it when it's convenient for you.
Just an alternative. I flush and fill coolant every 2 yrs at a cost of ~$10 per vehicle. Trans flush and fills cost me ~$25. Plugs are also cheap. It's just a little time. Diy allows me to maintain my car the way I choose and when I choose for significantly less than other alternatives.
It just seems odd to recommend that people wait a long time or don't maintain their vehicles. It's a huge expense like a house. Better to do some/more pm and keep an eye on stuff than little or no pm. To each his own though.
