What's the difference between Apple Watch and Apple Watch Sport?

Following the pricing announcements on Apple Watch, it seems that the "Watch" edition is priced 200$ above "Watch Sport" ($349 vs $549 for the 38mm model).

What are the features of "Watch" vs "Watch Sport" that makes it worth the extra $200 ?

I can read the spec sheet but apart from different band options and another type of front glass; I can't see what should justify such a large price gap.