You may not be aware of it, but the view command on (most?) Unix systems is basically a read-only way to execute vi. It has the same keybindings in general, of course, because it's actually the same program with the -R option, more useful than more or less. It's especially more useful because one can "break out" of the read-only limitations if necessary (and if one has the requisite permissions for the file in question), but one has to actively override those limitations.
Since the Web is, a lot of the time, basically a read-only medium with occasional need for limited editing -- and, when done well, it's a primarily textual medium -- the vi interface philosophy turns out to be quite appropriate. If you dislike having to switch interface contexts between keyboard and mouse because you're a touch-typist who has learned the efficiency and power of a keyboard driven interface for text editing, a browser that does the same thing is a very attractive idea.
Unfortunately, most people's experience of text user interface browsers is limited to the shite that has been available for more than a decade, such as the ubiquitous Lynx. While it's entirely keyboard driven, it's not a good TUI. It is, in fact, a crap TUI. Vimperator, however, has managed to improve on the failures of all other TUI Web browsers I've ever seen by importing vi idioms to the context of Web browsing -- improve on it so much that it blows away both TUI and GUI browsers, at least for me.
I also use a window manager with a keyboard driven interface, and I probably do more typing online than the vast majority of Web browser users. With all that in mind, keeping one hand on the keyboard and the other on the mouse would be broken up a lot by having to get my hands back to home row on the keyboard so I could do things like type in the browser, switch workspaces and do work there, and so on. At least 98% of the time, Vimperator obviates the need to keep one hand on the mouse the way you do it, which means there isn't any interface context switching going on in my brain at least 98% of the time for me, whereas without Vimperator I'd spend more like 60% of the time I'm using the Web browser also using a mouse and would have to switch back to home row every time I need to copy text to or from Vim in a terminal emulator (for instance).
Now, the only times I need a mouse in the browser is when I want to do something like click the upvote arrow here at HN or do something in a Flash object (such as start the Flash player, since I use Flashblock).
I used to believe that for the best browsing experience, a mouse was necessary for the majority of uses, because the Web is an inherently graphical medium. Even essentially pure-text pages seemed that way to me, because things like hyperlinks are location-specific. Vimperator has allowed me to learn the error of my reasoning in that regard.