When WDW began offering APs they offered a "Charter" AP holder status to those who purchased early in the program and a significant renewal discount has been carried forward for those with that designation. My understanding is that as long as those guests faithfully renew each year, they continue to be rewarded with the additional discount.
In looking at the chart at allearsnet it seems that the pricing of the DVC "tourist" charter is the same as the regular AP renewal for DVC members. The name used there doesn't sound very Disney-like but it does show the current pricing for the Charter Annual Pass.
Here is a link to information here on the DIS about current (as of 8/2/09) pricing for WDW admission media - including the DVC Discount on AP/PAP. The DVC renewal price is the same as the DVC discount on the Charter AP - but is still less than the Charter rate for non-DVC members. It appears that there is no additional price benefit over the regular DVC renewal price for those Charter AP holders who are also DVC members, but the price is about $45 less than it would be without the DVC discount.