These new tools are fairly different from the client-server applications of the 90s (and 00s and even now). Those desktop applications did have a lot of chrome on the client side, but the "real work" was being done on the server. Normal AJAX apps are more like those 90s apps - the UI lives in the client, but they rely more heavily on the server than a CouchApp would.

That said, all these Meteor and Firebase apps could end up having quite a bit of middleware and end up not seeming all that radical, depending on how much stuff gets added on.