Skype signed a deal with 3UK and Nokia to make the Skype software exclusive to many of their phones.
Skype boosts results for exclusive operators ? The Register
Skype on your Mobile - Skype
In the US they cut a deal with Verizon. So Skype is not available on Sprint, AT&T and T-Mobile, though there is a client for the iphone.
As for 802.11n. It is complicated. It can be transmitted over 2.4Ghz (like b and g) or 5Ghz (like a). It uses MIMO (multiple input, multiple output) basically it sends and receives many wireless signals at once.
It rocks because it has a much better range (typically up to 150 ft) and speed. N can go as fast as 600mbps, but 130mbps is the typical top speed of current hardware.
IEEE 802.11n-2009 - Wikipedia, the free encyclopedia
If you are lucky enough to have a large garden then you will definitely want n for your laptop and now your smartphone.
As the previous chap said you also need a 802.11n router. The current BT Homehub 2.0 (the small black shiny one) has 802.11n built in. The current Sky Sagem router only supports 802.11b/g.
Divx support means that the Desire/Droid Incredible will play back divx video files via the stock video player (You can find the video you have downloaded or transferred to the MicroSD card in the built in 'Photos' app).
Divx is the standard codec that is used to rip a DVD disc into typically a 700MB or 1.36GB file. For Films it is what MP3 is for Music. Despite Apple telling you different. People typically built up their divx collection by downloading torrents that they find on sites like The Pirate Bay, Torrentz and Isohunt. And they usually use a small piece of software called utorrent on their PC to download these divx files.
So I think I speak for every Desire and Droid Incredible customer when I say 'HTC please support divx'.