You can use Nessus to find machines with vulnerabilities, but I would not categorize it as a SIEM product. Arcsight is a full blown solution which includes a logger and correlation engine.

The emphasis that has been put on certifications is the biggest reason these vendors are not taking up a bigger share of the market. The industry standards for networking certs are the Cisco ones. Since the certs are catered to their equipment, it just makes sense that they…