I can't speak for all locals, but I don't believe that most locals are making multiple ADRs under multiple phone numbers. We also are not usually making ADRs 180 days in advance. The furthest out I have ever made an ADR (since I've lived here) was about 8 weeks, and that was for our anniversary. I made one about three weeks in advance last month because I knew I would be having visitors. But for myself personally, and I would guess most other locals, we are making ADRs usually just days in advance (sometimes on the same day), just taking what we can get, since we can be extremely flexible with times (I have an ADR for this Saturday that I made last Saturday) I would guess that not even 10% of Orlando locals eat at WDW regularly (I know we are the minority who do).
WDW already requires a CC to hold the most coveted spots--V&A's, special events like NYE, character meals, etc. Maybe they should add a few others to that list, like Le Cellier. But on the whole, requiring a CC for all ADRs is ridiculous. First of all, the reservation system itself would have to be flawless (twice in the past few months I have shown up to find that my ADR was "lost" somehow). Second, it would cost WDW to write software to put a cancellation fee program together, hire people to maintain the program, etc., and thus prices on tickets or on meals would have to go up.
WDW-DINE already will check to see if your given phone number has multiple ADRs for the same time. People who want to cheat the system and give a different phone number will always find a way to cheat the system no matter what, because they want to be cheaters and that is what cheaters do. I agree that if you don't show within an amount of time (I would say 20-25 min. is more realistic than 15 min., given that most vacationers are using WDW transportation), that you forfeit your spot. I really always thought they did this, anyway. And yes, if you know that you are going to miss an ADR, you should definitely call to cancel, go to Guest Services, or any TS podium to cancel. It's just plain rude not to.
WDW is making money at their restaurants whether or not Disney Ron or anyone else shows for their ADR or cancels ahead of time. There are always walk-ups to take those tables, and they do overbook ADRs anyway. As a business, they are not going to spend money on fixing something that to them is not broken.