i can see how outbound would be as the text for the link is on your page. Inbound links, by definition, are on some other page and therefor will not be a part of your own page keyword density.
All anchor text on a page is seen as page content. but forget about keyword density it's not a factor anymore.
It does not have the importance that it used to have, but too high density is still an issue for penalization, or triggering filters.
Im no seo expert but i can say. All text (outbound links included) on a page is part of your overall keyword density.. But definalty inbound links aren't part of your keyword density.. But the title text of the inbound links has alot to do with what key words your site will show up for.. Just dont overlook the fact that Inbound links and the title text are still highly important to your overall seo..