Non-OA is a multiple entry visa. "Reentry stamps" are only for single entry visas... Also, for the Non-OA you only get stamped in the as long as your insurance is valid for. If you reenter Thailand with 1 year insruance before the OA expires, you'll be stamped in for another yera.
A lot of people don't have the 800k baht (in their home country), so they do the Non-O in thailand and pay an agent here to cover the money. Also, you have to be in your home country to apply for it, which many people aren't/don't want to fly back for. Other than that, the Non-OA is the more convenient visa.
You people? You mean people under the age of 50 who still have their hair, a body fat percentage under 50%, and the ability to date women without having to pay them?