I own a bunch of straps too. While I think that Apple charges a premium on their straps, I'm sure that the quality and durability is not comparable on average.

For example, I got a couple of knock off silicone bands for my wife. They almost immediately started to peel and broke after a few trips to the ocean. The original ones seem to retain the same soft touch feeling.

On the other hand, Apple silicone bands are quite bad compared to Nomad sport bands.