An exceptionally nice feature of the major browsers is that they can normally handle 3 to 4 connections simultaneously. As long as these are small enough, they will appear soon after the text. Also, properly designed graphics can help minimize the size of the html file by moving some information into a separate connection, thus allowing the content to display faster. Also, when graphics are used, they can and should provide a significant visual enhancement to the page. Of course, text nav-links should normally be provided at the bottom of the page.
Users are normally interested in the content of the page.
Thus, plaintext users don't want to scroll through a pile of html links at the top. It's much better to read the page naturally and then follow the links when you get to the bottom. Of course, graphical browsers are more common, but those users also benefit from this organizational scheme. The content displays more quickly since there is no html heavy navlink section to load before the content. The client side imagemap code can be put at the bottom of the page, so that the content downloads first.