I think it's that everyone sets a good example. Disagreements really are differences of opinion; there are no ad hominem attacks. Posters are unfailingly polite and make sure to write so that they aren't misinterpreted. There's no attitude of superiority over non-bikers, or different bikers.

On other forums I read (one 99.9% women, one 100% women), posters disparage people with different opinions or practices, both other posters and "outsiders." For example, one woman justified her sneering at mothers who don't breastfeed by saying she had done a lot of research to determine that breastfeeding was the best choice, and that anyone who didn't breastfeed wasn't doing her best. It was that attitude of what's best for me is best for you that horrified me.

TE posters make an effort to write well. It's a personal peeve, and I probably miss some great things, but I can't read anything without standard capitalization, unless it's by e.e. cummings. Thank you for that from the bottom of my uptight heart!