Here's the figure from Asymco, quoting Apple chief executive Tim Cook, on the trajectory of popular Apple products in comparison to each other over the course of the products' respective lives.
The chart is a representation, rather than one produced by Apple.
Apple have sold 122 million Macs in the 28 years they have been available on the market. It sold 55 million iPads to date, and sold 22 million iPods in the first five years since the first device were out on the market. The company sold around 175 million iPhones to date, with 37 million of them in the last quarter alone.
In a nutshell: the iOS device collective reached 316 million cumulative units at the end of last year, while the Mac collective sold only 122 million cumulatively to date.
As Asymco puts it: "The iOS platform overtook the OS X platform in under four years and more iOS devices were sold in 2011 (156 million) than all the Macs ever sold (122 million)."
It goes without saying that there is a clear disparity between the Mac line of hardware and the iOS devices available. Not only in price, but functionality and availability. Apple has long been criticised for creating laptop and desktop hardware that is "overpriced" or "too expensive" for what you are given. It depends entirely on taste and what you want in a device.
But iOS devices are in an accessible league of their own, in that they are handheld, ultra-portable, and cheaper. They are probably more expensive in what they can do nowadays in comparison to what people need and want. The cultural shift has changed from desktops in the mid-1990's to laptops in the early-2000's, to handhelds towards the mid-to-end of the decade.