Then I'm an idiot too, because I don't understand completely either.
But UDP and HTTP are just 2 formats that are used to transfer data across a network, ie user datagram protocol and hypertext transfer protocol. I'm not completely sure why, but it seems like HTTP (which is also used for web page communications too), seems most commonly used for live streaming of video data, and UDP seems to be more applicable for transfer of files. I'm not sure which format is the fastest. With my Roku HD1000, HTTP streaming is significantly faster than UDP streaming, however with the Azbox, it seems like UDP is about twice as fast as HTTP, so I'm guessing that the differences must be mainly in the efficiency of the programs doing the streaming more than the specific protocols. BTW, there are a lot of data transponders on satellite that are sending IP/DVB type data, and if you have TSREADER, you can see the specifics of the transfers. Whenever you see a handfull of mac addresses with high IP#s, starting in the 224.x.x.x range or 239.x.x.x, these are often transfer of video by UDP format, whereas if you see a bunch of mac numbers sending in http format, it's usually regular internet transfers.
I am not sure about this, just guessing, but I get the impression that UDP is usually used within a LAN rather than over the internet, and is usually used for binary data, and I THINK that UDP involves less overhead of communications between sender and receiver, and may be a little less reliable relative to errors. I also think that UDP can be used to send to multiple receivers, but I have no idea of how that works. I do know that sometimes if you find a UDP stream on sat, that sometimes you can have that stream repeated over your network, and VLC can play the video if you key in the proper destination IP#, but usually you can't do this because the data is often in proprietary formats.
Anyway, I'm really confused by the differences between these two formats, because it seems like UDP would be better for streaming live video, but it seems like HTTP is what is used, and I don't have a clue why.