[d4mi3n]

While I share the sentiment, there are plenty of perfectly valid reasons one might need or want to do this--I can't comment on that particular article as it seems to have moved off the front page.

A few things that could justify rebuilding the wheel as it were:

1. The thing doesn't work for the environment it's being used in (corporate network, obscure mobile browser, screen reader, whatever)

2. The thing doesn't work for non-Gregorian calendars

3. The thing doesn't work consistency across various types of clients (this reason gives me some nostalgic flashbacks to the early days of jQuery)

4. The thing is fine, somebody just wants to see how the sausage is made to learn of it

There's probably other reasons one would want to re-invent a common UI element. It's really hard to say how objectively good or bad a particular attempt is without context and more clarity on what metric it's being judged by.