Sure but how is this not a "variation on a theme"? The iPod and the iPhone were hugely impactful despite, in some sense, merely being variations on a theme. I'

Sure but how is this not a "variation on a theme"? The iPod and the iPhone were hugely impactful despite, in some sense, merely being variations on a theme. I'm all for the safety bicycle being considered very significant historically, but it's no less a variation on a theme (technically or scientifically) than the iPhone or the iPod.