Most, but not all, commercial wristwatches use standardized lugs of standardized sizes, allowing you to install off-the-shelf straps, bracelets, and whatnot from any watch onto any other. I've currently got a 3rd-party nylon strap on my Moto 360. No big deal. Many people who wanted a metal bracelet installed the aftermarket Pebble bracelet on their Moto watches. Perfect fit.

So, yeah, I'm just not all that excited by Apple Watch straps. They're straps. For a watch.