The reason eBay and Craigslist suck, is that you post something that interests people, and you open your email box to find 12 basically identical questions. Then you have to email each person, many of whom are tire kickers anyway, then modify or add to the listing. Chances are some people looked at it 2 days ago, and they decide to email you without re-reading the ad carefully to see the changes you made. The beauty of an open forum is people can HELP you sell your stuff. You might be selling a set of wheels, and someone will ask you the offset, ask if there are any cracks, and if they will fit a 1989 MR2. You post that info up and everyone sees it. Who wants to wade through a full PM box every day, especially for threads with multiple items?
I can understand limiting thread bumping within reason, and the issue of people shitting on others threads seems to have already been taken care of with promise of (IMHO appropriate) consequences. But it seems the majority of forum members want to let people respond to their ads, so why force a new system down everyones throat when they don’t want it? Just my $.02.