We chose Apache as it is the common front-end to the rest of our stacks (the idea is that you can mix and match all the apps in our library and serve them through a common Apache frontend). Regarding performance, what you mention is correct with older versions of Apache. Apache 2.4 with the Event MPM is pretty much equivalent to NGINX in terms of performance and memory footprint.

Having said that, we do include NGINX in some of our other infrastructure stack and we plan to expand its usage (as well as provide other NoSQL engines, we just started with the most popular :)