Is the web browser the best technology to achieve "multiplatform" for an office suite? It makes sense from a purely practical sense but technologically it's pretty terrible.
I wrote pivot table functionality in XSLT and XML for IE6. Pretty much 10 years ago. It's not that you couldn't do it, it was that it wasn't worth it.
Your whole multiplatform thing is disingenuous because back then there really was only 1 platform. Windows. So you've conveniently forgotten about the lotus suite, etc.
I also think you're vastly overestimating how far we've come in that timespan. Like v8 was pretty much 95% of the improvements, simply because you could do more than 1000 loops in JavaScript without killing the browser.
And yet today it is still harder to make a decent web app than it was in VB6 15 years ago.