In response to my Ajax rants, Mark Finkel points out browsers can do rich graphics using SVG and VML.

Frankly, this is the direction the web needs to head.  I am a big fan of these vector graphics formats (my friend Richard See and I  launched Visio's SVG efforts).

The problem is neither SVG or VML have ever been fully accepted and supported.  The browser wars ended (temporarily) and the two main combatants stepped back from the field just before a vector graphics format was standardized.  This has left a gaping hole in web development which Flash has rushed in to fill.  If Mozilla does a great SVG implementation, the game may change...but that will something new, call is Ajax-S (Ajax with SVG).  The hype and excitement about Ajax is that it runs on what is 99% supported by browsers today.

The adoption issues aside (which issues Avalon, Xul and other new Rich Client platforms also suffer from), I claim SVG and VML are not currently good enough or integrated enough to build Office-like applications.  I should know, because when I was at Visio we tried, and I've talked to others who tried similar things.  Perf is terrible and  the programming models are impossible (you can do great server-side generation, but working from JavaScript ala Ajax is a nightmare).

As an aside, my best friend designed a vector graphics format for the web over 10 years ago, and Mosaic actually was supporting it...just as Netscape tore the browser market away from them.