No official documentation. I know you don't support it, but its always helpful to have a nice starting point when writing rules. After reading about 3 separate threads on IPS about Nginx, I finally wrote my own modified rules, which I've yet to test since I'm too nervous to make the move. I'll have to setup a test site and mess around, but thats besides the point.
Hell, Xenforo even gives out IIS rewrites and lighttpd.
I personally think this could very much separate you from the competition, especially as times are changing. More and more people are moving away from the basic mySQL / Apache to things like MariaDB + XtraDB, or lighttpd / nginx / varnish / squid.
I don't know what everyone is getting up in arms about.
I had IP.Downloads expire 5 days ago. IP. Board expired today, and IP. Content had been expired for a few months. I paid $50 and all of sudden all my products are on the same billing cycle. Now I just have to worry about 1 date every 6 months. This isn't complicated. Read the information you are given and stop making assumptions.
IPS isn't cheating anyone nor doing any black magic. Their system makes sense. Read the website. Read the client area. It all makes sense if you just read it.