"No AH.Com" would have absolutely no effect on the "real world". However, the presence of AH.Com has allowed many bright and well-informed people to satisfy their desires to see their ideas in print and discussed in a way that is far easier and less restrictive that publishing them (either self, online, or through publishing houses). While that is good, one also wonders if the authors of some of the really good alternate histories on this site might have made serious (and possibly more financially lucrative) attempts to see them published for the broader world.
I found this site in 2003/4 when there were a variety of small websites, message boards, and blog sites featuring alternate history. AH.Com was easy to join and contribute to and (this will sound condescending to newer members, sorry) overall had a higher percentage of serious contributors. It obviously was placed to capture a market for people who thought a lot about historical "what ifs" and was very welcoming to them. Maybe another site would take this place...maybe not.