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I call BS. On most every web project I've been involved in, we've used progressive JPEGs for the size optimization. This was crucial in the dial up modem days when we were inventing how web sites should best serve users, and we still do it. Sites with faster times to perceived page completion consistently drove higher page views and longer times on site. Even in browsers not supporting progressive rendering, perceived completion was faster due to smaller size meaning faster load time. Switching from baseline to progressive consistently drove higher page views and longer times on site.
I have never heard a single client say a single user complained about progressive JPEGs. I'm not saying it hasn't happened somewhere to someone. Users will complain about anything. But in billions of page views across countless clients (including pro photo clients), I haven't run into user complaints from progressive JPEGs, only measurable page view and time on site improvements in user behavior.