Landlord gone crazy?

We live in a large apartment building, and today, on August 8, I noticed that the landlord had posted "Notice to Quit for Non-payment of Rent" notices to the doors of at least 15 units! Ours was included--we had told him that one of us moves out and the other stays with another roommate, as August 31 is the end of our lease. He had said that is OK (in July), and one of us then would use his last month's rent for August. When I asked him about the notice, he said that he had forgotten (although we also gave a written notice on August 1), and asked us to disregard the notice to quit. Now, my question is--how is that possible that about 15 units out of about 70 receive such notices in a single day, in August? Are all of them people who use their last month's rent for paying for that month, and the notice to vacate the premises in 14 days serves the purpose to give the landlord more time to "refurbish" the apartments for new tenants who move in? Is that sort of thing widespread and legal?