What these companies worry about is not free information. Their concerns are usually around company IPs, copyrights, reputation/branding...etc.

Do those risks exist? Sure. But it's silly to blindly forbid your employee's outside-business activities like this. However, in this job market, employers probably can easily find candidates that don't have problem with this silly restriction so they don't have incentives to allocate resources to deal with the headache.

A personal website may sound too "professional" to a legal person. I bet OP could post the same information on facebook/twitter without getting into any trouble.

No kidding, what an absolutely stupid thing to do as an employer. I (badly) want people who are so interested in the industry that they will research external information and write about it. The correct response for the employer should have been at minimum gratitude and encouragement. Threatening legal action falls under the old adage that "no good deed goes unpunished."