They only said they were adding a year and a half ago. I'd like to be anti-social without appearing I'm anti-social. I'm also fairly sure most people would prefer to be anonymous from time time to for whatever reason. I know D3 has a bunch of MMO devs who think forced socialization is the bestest thing ever...but seriously...sometimes we want to be left alone.
“Appear Offline” Option Coming Soon to Battle.net
Note the date.