Yes, there are certainly things that get posted from live hands that aren't really considerations in online poker. I mean there was a post the other day where the flop went 7 ways... I played like 4 million hands of full ring probably and I don't think I ever saw that once. It's just totally different. I played in this 5 card PLO game at work for a year and we'd have everyone see a flop in a raised pot soooo many times.

As to your actual question of whether online players realize the impact this can have on the strength of your hand/range vs theirs, I think they do but they just might not have as good an idea of the magnitude of difference caused by n players seeing a flop where n is a number that just doesn't occur often online. But this as you stated is most likely do to little experience with said situations, opposed to just pure negligence.