Apart from the Adaptive Media Streaming feature, all the "plus" features seem to be stuff that anybody can have with the open source version and some external scripting/integration:

* Application Health Checking -> Nagios * Monitoring -> stub_status_module + Munin/Nagios * Advanced Load Balancing -> Chain Varnish / Nginx * Dynamic Configuration -> Seamless configuration reload without service interruption is possible in the open source version * High Availability -> Pacemaker or whatever...

That's stuff that high traffic sites have covered themselves. But: Many normal Enterprise IT ops won't touch Nginx with a stick if they can't pay for it and have someone to blame should things go wrong. Plus, managers love shiny dashboards, buzzword features and fact sheets like http://nginx.com/media/cms_page_media/21/nginx_plus_datashee...

Everybody wins.