What the Heck is Leap Day, Anyway?

There a poem of sorts that addresses Leap Year and I'm sure we're all familiar with it. It starts off like this:

30 days hath September,
April, June and November,

Not a bad start for a poem. It's short, it rhymes and it's easy to remember

Nice couplet there. the poem continues:

All the rest have 31,
Excepting February alone.
Which only has but 28 days clear
And 29 in each leap year

What the hell happened to the rhyme scheme? It's like they just gave up when it came to explaining Leap Year.

Well, in case you are having trouble with exactly why we have leap year at all, here's a great little video that does a great job of explaining that phenomenon.