Users don't scroll
On the Web, the inverted pyramid becomes even more important since we know from several user studies that users don't scroll, so they will very frequently be left to read only the top part of an article. The Web is a linking medium and we know from hypertext theory that writing for interlinked information spaces is different than writing linear flows of text.
Split Web texts
Web writers should split their writing into smaller, coherent pieces to avoid long scrolling pages. Each page would be structured as an inverted pyramid, but the entire work would seem more like a set of pyramids floating in cyberspace than as a traditional "article". Unfortunately, it is hard to learn this new writing style. I am certainly not there yet myself, as you can see.