Support for IE (and other browsers, especially Safari) is certainly an important area to cover. Since the article's topic is the future of Linux distributions, however, the focus is on Firefox, X windows and anything that runs under a Free/Open Linux or *BSD system. Of course integration via Java applet (e.g. VNC, NoMachine NX) can be cross-browser.
In addition, Firefox 3.0 will have some very impressive features for SaaS. If a "killer app"
emerges that takes advantage of these facilities, it is not inconceivable to require installation of a free browser to gain improved functionality -- especially in organizations.
Currently, alternatives to the browser seem underdeveloped (if they exist at all). Contrast this with using Python, for example, to replace the shell and friends. Here, the alternative is highly mature, so the migration path away from the older toolset is clearly visible.
Of course, if you are aware of any sufficiently capable and mature alternatives to the browser, feel free to discuss them.