Yeah, the same thing happened to my Apple TV this morning. I even restarted it just to see if it was that kind of issue but the TV shows icon is still missing.
Turned my TV on and I saw the TV Shows icon disappear instantly, then came here to see if anyone else had the same problem. Obviously this is a widespread issue. Guess we just wait for Apple to correct it.
But hey, as a compensation, there have been 5 new ones added to the bottom of screen!
Disney Channel, Disney XD, The Weather Channel, Smithsonian and Vevo. At least for me.