I'll chime in with my personal experience for what it's worth. I have a HUO Spiderman, second owner, had 200 plays on it when I got it. Over 1500 now. Also have a HUO LOTR, second owner, had 1000 when I got it, over 2000 now. Zero dimpling on either machine. I just got a Star Trek Premium brand new in box, first new machine I've purchased. 41 plays, lots of dimpling and new dimples with every ball.
Clearly there's a difference in the hardness of the wood used. No one will convince me otherwise. Did Stern (or the playfield contractor) consciously use cheaper wood or is it just a random variance in available material? Who knows. It's not going to stop me from playing the game, but I'd be lying if I said I didn't find it really annoying. It annoys me because clearly it doesn't need to be this way as evidenced by my other two Stern games.