What's really noticeable is how prevalent those in the food and hospitality industry are. Not only are there a lot of them, they have consistently big followings and are very active.
Every now and then I find Twitter accounts from other businesses. But they're comparatively few and far between. And they're usually not up to date. Most of them signed up long ago, tweeted a few times and just gave up!
Cafes and restaurants sell social experiences
I'm not sure exactly why this phenomenon occurs but I think it's got something to do with the fact that cafes and restaurants need to create an atmosphere in which patrons can chat and enjoy each others' company. They are selling a social experience already, and therefore take to social media like ducks to water. They also thrive on regulars. So they're keen to create and maintain a friendly rapport with customers online as well.
Businesses in other fields tend to be more about supplying products or services that don't require any social interaction -- and often just once -- so they don't see the value of Twitter. That's unfortunate because it's certainly a quick and effective way to increase your online footprint as well as get more people in your city to know about what you do. (If you wish, I can quickly show you how to do this in a private lesson or two.)