I think the author is almost right: Google's vulnerability is its dependence on advertising for its revenue stream, but I don't think widespread adoption of ad blocking software is very likely: most people don't care, and/or don't have the knowledge to install browser extensions. Text-based ads are also harder to block, and it will just lead to an arms race in which only a small portion of users will bother to take the measures necessary to block all/most ads.

But I do think Google is vulnerable to a collapse in the web advertising market. Look at all the pain that was caused the last time this happened (didn't we learn our lesson about building businesses that are totally dependent on advertising income?). If the advertising market were to collapse, what would Google do? (I'm genuinely curious to hear speculation about this...)