You're right that it's just as durable as any other product but it will have a lot of scratches and some people don't like seeing so many scratches on their new iphone. Even the iphone 7s that were on display after the Apple Event already had scratches on them.The glossy black is actually very durable on other Apple products. It's the same aluminum material used on the Mac Pro which is a very solid machine. I also imagine it's made with the same process as the space black Apple Watch.
Apple warns new glossy Jet Black iPhone 7 finish will scratch easily, recommends using case
https://9to5mac.com/2016/09/07/apple-warns-jet-black-iphone-7-scratches/
Hidden in the fine print of the tech specs page for iPhone 7 is the following warning:
The high-gloss finish of the jet black iPhone 7 is achieved through a precision nine-step anodization and polishing process. Its surface is equally as hard as other anodized Apple products; however, its high shine may show fine micro-abrasions with use. If you are concerned about this, we suggest you use one of the many cases available to protect your iPhone.