topfs2, the advantage Apple has is size, popularity and relatively slow rate of feature growth. If you don't know how to do something on the iphone you can google it and you will find the offical apple support pages, the official apple forums, about a dozen apple fan boy forums, half a dozen blogs/guides/articles and hundreds of other forums that maybe able to help (ie tech forums).
XBMC has this forum and its wiki. Both of which are good but neither are as extensive or up to date (due to the higher development speed) as the apple 'support sources'.
The other problem with comparing an iphone to XBMC is people understanding of each systems capability.
Iphones have thousands of apps, for nearly all everything and apple markets it on that basis (“There is an app for that”
and people understand that when they buy an Iphone they can do as much as they want, they just need to search for the app.
Whereas with XBMC the assumption of a new user is likely to be “XBMC can’t do blah blah” as they don’t know any better.
As a relatively new user to XBMC I know how hard it is to actually find out what it is and what it does (in detail, ie why is it better than Windows Media Centre/Myth/Media portal etc). In the end I just downloaded it and played around until I figured it out.
I think there needs to be as much (sensible) publicising of XBMC’s features and capabilities as possible, especially if those features aren’t included in the initial download, people need to know there is something to look for.
The idea of listing the official addon repo on the main site is (imo) a great idea, similar to the way Firefox does with their extensions. You could also follow their example with the highest rated (as suggested above) and possible a ‘Recommended by the Dev Teams’ list. This list could highlight either the more advanced and plugins (Grooveshark) or ones that give a real unique edge to XBMC (Launcher or some of the remote control apps).
Edit: I don't mean to sound negative, the addon manager is a great addition, but I just think that it should be clear to the new user that the download is pretty bare and a lot of the features are 'unlocked' via the addon system.