Thanks for going to the effort of asking developers to make their applications work better with Ubuntu!
Application indicators work not just “starting with Ubuntu 11.04”, but starting with Ubuntu 10.04 LTS.
I suggest not referring to “the Ayatana design team” — developers are unlikely to know what that is, and it isn’t relevant to your point. Just say “Ubuntu”.
If a program has a “system tray indicator”, then it’s already doing the right thing and you’re using Gnome 2. I think you mean “notification area item”.
“with application indicators they can be addressed” … Well, are they? This could be much shorter if you just said “More accessible — works better with screenreaders”, or something like that.
https://wiki.ubuntu.com/DesktopExperienceTeam/ApplicationIndicators includes a lot of information that is interesting only to developers of Ubuntu itself. I suggest leaving it out, especially since it’s already linked to from the unity.ubuntu.com page anyway. And the “What do I need to tell a developer” page doesn’t contain relevant information (and reads more like campaign organization than documentation), so you could leave that out too.