IIRC valve removed that because it was used to scam people not knowing the /me command into believing that because the person had different text/color it must be a valve employee/some one important.
Case and point:
http://www.dansdata.com/images/blog/steam_chat_phish.jpg
If that is the case, I will miss having it. I did not catch wind of any threat reduction from Valve themselves.
See here http://steamcommunity.com/groups/SteamClientBeta/discussions to petition for the feature to be restored (in a fixed manner)
I personally do not see an exploit here, phishing for someone else's password is equally violating the TOS with or without using /me and there is not a track record of valve employees randomly contacting users via PM. Just because the lame user is phishing with a new tactic does not mean the system is at fault.
Closing as this was a deliberate change and isn't a Linux issue. The petition link above is the place for further feedback.
Nothing extracted yet.
Pretty self explanatory, /me used to be able to be used for expressing actions, and no longer triggers it's action in chat and PM.