Web developers should be in the habit of checking against many different configurations anyway. I've lost track of the number of times that I've stumbled on a scrollable area that wasn't meant to be scrollable, which would have been caught if the developer had opened the site in the browser with always on scroll bars.

You raise a good point. Fortunately, I'm not a web developer but I will keep your point in mind in case I do any web development later.

From a web development standpoint, the scrollbars do seem to be an ignored feature for a lot of web pages. Adding scrollbars actually fixes a lot of issues with some sites. For example, some sites often have a frame inside of another frame, and this reveals the scrollbars for both frames. If I were to use my mouse wheel, I might scroll down inner frame or the outer frame, and I wouldn't know which one would be activated until I try, but with the scrollbars on, I always know which one is which. This was a surprise benefit to this change.

That's why I still develop using pluginless Chrome, even though I've always used Firefox as my default browser.