The reason? iOS 7's "frosted glass" effect.
Apple's new operating system for iPhone just got a bit too much in common with Windows Vista, the much-berated 2007 update to Windows XP, he thinks. (XP, of course, was perhaps Microsoft's best operating system ever, and many who transferred to Vista regretted the update.)
Vista's main visual update from XP was that its folders all appeared to be made out of frosted glass:
In terms of iOS 7, Apple has done kinda the same thing:
Goeldi's point is not that frosted glass is bad in and of itself. Rather, when Microsoft introduced it into Windows, it signaled that the company had stopped innovating the system in a genuinely new and useful way and was instead tinkering with style details that no one wanted tinkered with.
Apple, he suspects, may have reached the same peak: iOS is a great operating system. There may be diminishing marginal returns in improving it. So the easiest way to make it "new" is to tweak its looks.
Thus, frosted glass = lack of innovation.