Hi, I was checking in for my flight to JFK from DUB last night and I got the following message

>>We are seeking volunteers willing to take a different flight in exchange for a travel voucher.
If you're interested in volunteering, you can get more information at the departure gate for your flight to New York.

So I got to the airport in plenty of time... hoping to get bumped to the ATL flight (Infact im sitting in the terminal now).. and when i asked at the delta desk + checkin, I was told "the flight is not oversold.. we dont need to bump any passengers. However, I just checked online again, and it again presents the message (above).

Is this common?
Cheers
D