It's going to take a long time for Chrome to get the same kind of third-party developer support that Firefox already has, but I don't think that's Google's objective: I think that they're targeting users who want simple, fast browsing, and couldn't care less whether the browser supports add-ons. Click one button and it's installed. Every visitor to Google Search is a potential user. That's got to scare Microsoft, even if Chrome is less sophisticated in many ways than IE.
I've visited some sites that don't recognize the Chrome user agent, and thus either limit access or won't give access to Chrome users at all. Therefore, the onus is now on Google to get site developers to support Chrome. That's not going to be easy, because other than the Google name, I haven't seen anything compelling enough to get most people to switch from their existing browser to Chrome.