Well, it's important to remember that the significance of the links isn't simply as copy on the page being spidered, but as links for the spider to follow to the pages they link to.
Depending on the nature of your site, it's likely that something other than the home page will be targeted towards a given specific search - and the link to that page helps in that targeting.
For instance, if I have a site about generators, my home page might give an overview of the types of generators I sell, but it will also link to a page specifically on PTO generators. That page will be SEOd for searches on PTO generators, both in terms of copy and in terms of the link to that page. An image won't help the
SEO on my PTO generator page as much as anchor text of "PTO Generators" would.