There wasn't much of a window where we had the ability to reliably dynamically update webpages without a way of getting data to do it. IE4 was the first browser that had a modern dynamic DOM with CSS support -- but it was all very rudimentary. IE5 came out a little more than a year later came with MSXML 2.0 which had the Microsoft.XMLHTTP ActiveX object that could be used within the browser; so it was really only like 14 months where we had DHTML without the ability to do XML HTTP requests.
And even then, you couldn't really make use of it unless you were in the enviable position of not having to maintain Netscape compatibility, because Netscape basically had no ability to alter a page after it was loaded outside of extremely specific exceptions like being able to replace one image with another image of exactly the same size. And through the weird and broken 'layers' concept they came up with to try to rush out a response to IE's iframes.
I remember discovering Microsoft.XMLHTTP in early 1999; probably within a month of IE5 coming out, and it really was like suddenly gaining a superpower. People (rightfully) gave Internet Explorer a whole lot of crap for getting to IE6 and then stagnating for years; but so much of what we consider to be the modern web today can trace its lineage directly to the ideas Microsoft brought to the browser in IE4 and IE5. They basically reinvented what the browser could be.
