I'd say they're right. The web is expanding markets. The remaining fraction of the market after the giants have had their lion's share is still larger in the 'web' world - perhaps not in percentage terms but in absolute dollar terms. Which is what matters.
I'm not going to say that technology hasn't changed anything - it's doubtless opened some things up. But where there are big network effects, it is still going to lead to a dominant player in a given market. Where there aren't, there is room for more competition. That's always going to be true, whatever technology you're talking about.
“Ignore basic economic principles at your own risk. Technology changes. Economic laws do not.” -- Hal Varian (who is now Google's Chief Economist)
http://www.squeezedbooks.com/book/show/7/information-rules-a...