A mobile app makes sense for one reason: geo-location. Your phone knows where you are, so it can find lunches instantly without having to do anything. And that's the one thing you keep with you on your way to lunch, you don't carry your laptop around usually :-)
EDIT: also, notifications are important, you want to know whether your lunch is on or not. Emails would work too, but that's kind of old school.
EDIT: also, notifications are important, you want to know whether your lunch is on or not. Emails would work too, but that's kind of old school.