It's not just forums. So many things, both internal and external at HP are like that for some weird reason (for a very long time now)
holy cow.
A former HP employee told me that a creating named subdomain required a VP-level signoff, while those "license plate" style subdomains could be provisioned by almost anybody via a self-service tool. So if there isn't a real reason for a nice URL, people tend to create license plate subdomains.