In this context the comparison is not about the quality of IE6 as a browser, but the control it allowed Microsoft to exert on the internet ecosystem by virtue of its market share. Chrome is now in the same position, holding the vast majority of the www "hostage" to the whims of Google.
The longer Chrome stays popular, the more websites will optimize for Chrome, bringing back the days of "Best viewed in Internet Explorer". And as more and more sites become accessible only in Chrome, user share tilts further in Chrome's favor, and so on in the vicious cycle we experienced in the browser dark ages.
That's the fear, at least. I don't think anyone is concerned that Chrome is going to start BSoDing Windows anytime soon.
The omens of monopoly are certainly here, though. All of Google's websites, which constitute a large percentage of web traffic, have been a "best viewed in Chrome" affair for a few years now. Microsoft recently dropped support for Firefox on the Skype web client. And I've seen my fair share of niche/corporate/etc websites that are Chrome-only.
(FYI, I'm not personally worried that we'll see the same browser dark ages as before, but it's something we should be vigilant against.)