It's about the little differences sometimes. It strikes me that businesses that begin from small roots, tend to grow into friendly work environments, rather than impersonal corporate office cubes.
A sole-trader gets their first employee. In all likelihood, they eat their lunch together, whether it be packed lunch or a nip out to a sandwich bar.
You're likely to be talking about your current project. Lunch provides you with time-out, helps you to see woods from trees. Sad? No, I say productive.
You expand and pull in a couple more members of staff. A small office is unlikely to be the best place for you all to eat lunch, but by this time maybe you have a larger place and you all end up around the meeting table.
I remember some of our group meetings at uni would be based around meal times. :)