That's the first thing I thought. Is that part of the minimalism? An oversight? As a used an April with 31 days makes me question the basic competency of the site, I'd relate it to poor copy. However, I do adore the stripped back aesthetic, and I hope this demo can inspire some UX evolution for calendars.
You're deducting points because of his excellent consistency?
"A foolish consistency is the hobgoblin of little minds" -- Emerson
Hobgoblin was my favorite superhero in the DC universe.