Apple Watch Strap Pricing structure doesn't make any sense

I'm a bit confused by the pricing structure for the Apple Watch. I like the 42mm screen and the base price with the sport strap is £339. However the strap i like is the space black stainless steel strap, which is a whopping £949!!! For a minimum diffference of £610 for the space black strap, what can the metal strap do over the sports strap to warrant a strap cost of this much?

Oddly the normal silver metal strap is £859, so the strap upgrade for that is £520. Strangely i could get the 42mm Sports watch, for £339 and then buy the silver metal strap for £379 (you can't purchase the space metal black strap separately), that makes the purchase £718, a saving of £141, plus you get 2 straps for less.

Maybe I'm getting my maths wrong, but the costs of the straps are putting me off.