So you delete every OT comment, every comment from people saying they will be gone, or wishing people Happy Thanksgiving, or have a nice weekend, or whatever. Your criteria is that if it is not about the company, period, you delete it.
Yes, all those posts are able to be deleted according to the rules, but there's no rule they must be -- just like not every speeder gets caught, and you can't tell the judge there were others speeders who got away. Shelly describes this art very well here: #msg-21736555
One mark of a successful moderator group is finding that very fine balance of keeping the board engaged in discussion of the stock while allowing some, minimal friendly dialogue amongst the users.