> Blogging seems to be an unhealthy activity for physicists.

This kind of observation is valuable, I think, even if it's only statistically true. Certain disciplines encourage practitioners to work within conventions and with capabilities that closely match the activity of blogging (or being on Twitter). For other disciplines, tweeting/blogging is very far from the core competencies, so practitioners who do pursue it are more likely to be outliers.

The other, not-so-neutral aspect of this is the narcissism problem. People who do a lot of personal PR are more likely to be narcissists—and this is a more negative indication in disciplines where self-promotion is an anomaly.