Never raise pre-flop?

[bige321786]

Hello everyone, as this is my first post here at 2+2.
I've been a reader for quite a while now and I thank you all for your lively discussions, questions, answers, theories, etc.
My question concerns raising pre-flop in low-limit, usually loose-passive, limit texas hold 'em games. I am a frequent B&M limit hold 'em player, and play recreationally anywhere from 3/6 to 9/18. Although I play recreationally, I do take the game seriously and am always trying to study the game, plug my leaks and improve my play.
There are two older gentlemen I play LHE with very frequently. I've probably played with each of them for more than 10,000 hands each. I've noticed they both play similarly and both play particularly well after the flop. Both of them hardly ever raise pre-flop. One of them only open-raises pre-flop with QQ, KK and AA, and will never re-raise, while the other will ONLY re-raise with AA (meaning, he will not open raise with AA; however, he will re-raise with AA pre-flop).
If you play particularly well post-flop, how much edge, if any, are you giving up by not open-raising at all pre-flop?
I am much closer to one of these older gentlemen than I am the other and I have talked poker with him quite a bit. His wife passed away, he lives near the casino, played poker all his life and enjoys the social atmosphere of the card room. He plays about 30-40 hours a week and says he makes about 1.2BB/hour, playing mainly 3/6, 4/8 and 6/12.
I understand the theoretical reasons for raising pre-flop, but how much does that matter in very loose, usually passive, limit hold 'em games?
Thank you very much.