Most webfilters subscribe to list services for domain categorization and reputation. If this domain makes a listed category that is filtered, bam it's blocked. Or your admins could have manually added it due to peaking their interest. They can also white list it if it does make a list or is incorrectly categorized in their flavor of filtering/proxy.
I don't see this domain blacklisted on spamhaus so it's probably your local yahoos dicking you. Submit a ticket and tell them you use it for research.
It does have some issues and any of these could get it categorized by your filter to block it, especially dns serials not matching.
Most webfilters subscribe to list services for domain categorization and reputation.
Irate could have been flagged for your company firewall software.
They could have looked at the number of hits and determined you spent to much time there.