I didn't know about mcmaster.com, but I took a look at it, and the images was a surprise. The uniformity of the product images is nothing sort of amazing.

Most websites don't care to much about illustrations, even though that's what many people use when buying. Taking your own photos, or doing illustrations is pretty expensive, but it really helps the customers pick the right products.

The grayscale may be a way of insuring that customers aren't overly focused on the illustrations, and instead actually read the product descriptions.