Any day can be Doughnut Day if you try hard enough. Honestly though, I love any opportunity to talk about doughnuts, and would like to use this holiday to bring awareness to my favourite summer dessert: grilled doughnuts.
Store bought muffins are huge, and full of sugar and calories. That makes them a dessert, a treat, an indulgence - at which point you might as well get something tasty like a doughnut instead. Bonus: the doughnut probably has less sugar anyway.