Well its their slogan.
They want to use the photos for their advertising campaign. Print on their brochures etc. A theme like "Food Glorious Food" would yield images which are useless to them.
Its a very good idea actually. They get a whole range of photos to choose from, many professional to use for their ad campaigns. Whereas it would cost them about the same amount to hire a pro to do it, with far less variety and choice.
I don't see this as milking photographers and I'm not against it... gives small time photographers a chance to shine. Else contracts such as these will go to the established names. Of course if you're a professional photographer, you'll shun this. Takes away yr business and makes you compete for your $$, rather than hiring you outright which is guranteed income.
Of course you could argue that pros work hard to establish themseleves, and its only right they harvest the fruits of their labour, in terms of being sought after and hired for lucrative projects.