You also have Red5 which is open source and rocks very much. It is just a -tad- less reliable than Wowza which you can't really sell to paying customers, but it's much more fun and customizable.
And to answer your question, Wowza is just a cheaper FMS which also supports other platforms next to RTMP. This article is basically taking the more performant HTTP download mechanism for static content (like YouTube uses) and then hacking it to put a live stream in it instead.
In terms of licensing, it is $55/mo/instance or $995 for a one-time license.
There are also EC2 instances that start at 15 cents per hour.
Much less expensive than FMS