It seems to me that many old-school gamers feel that the retro-clones should be put in some kind of straitjacket, where as little deviation as possible is allowed. While I support the games being 95% the same, I really prefer the ascending Armor Class as introduced by DnD 3e.
Ascending AC is much easier to use in game, and very easy to explain to new players. It also is very friendly to math-averse players, as they can see the number they need without having to look at a table. It also takes up a lot less space in the rulebook, as you just need to add the Base-to-hit number in each class chart, and don't need another half to full page chart for players. In addition, just having monster BtH equal their HD will save an additional chart in the game, and makes it even easier for the DM.
I understand that many DMs want the old style, as then they won't have to do any conversions of older modules. But at least a few of them are fairly strident in saying that Ascending AC should not even be included in the retro games. It's the "Stay off my lawn!" syndrome. And it seems to be fairly prevalent in older gamers. I believe that having Ascending AC as the default, or at least as an option, will help bring in newer ex-3e players, as it's something they are already familiar with.
And like it or not, I think the Old School Revival needs at least a small influx of new players as time goes on, or it will sputter out and die in a few years, which would be very unfortunate. The current grognards aren't getting any younger, and to maintain at least some type of player base, new people, preferably younger, will be needed. Of course, this is looking at it from a publisher viewpoint, and not a gamer viewpoint, so many grognards will happily say they need no new blood, as long as they get their 4 or 5 new modules every year.