Let me present some highly partial and unscientific evidence to support my point: Mrs GB's laptop. For her high-powered work, she just had to have a commensurately high-powered laptop and ended up purchasing a Dell Precision – for an eye-watering £1,600 (or thereabouts). The monitor was £200 extra. That was three-and-a-half years ago.
A year later, I purchased a new PC too – a proper, manly desktop for around £900, including a big, fat monitor, from Mesh.
Mrs GB has a dual-core laptop. I have a quad-core PC. We both have 4GB of memory, but I can upgrade to eight for less than £20, whereas hers would cost more than £120.
I have a 1TB disk, whereas she has to cram in some sizeable applications on less than half that amount.
I also have a much more powerful graphics card and, unlike her, I don't need to open up the box on a regular basis to clean the carpet of fluff out from the fan. Nor does the PC overheat, unlike the laptop, and it's also quieter.
That's not to say that smartphones, tablets, ebook readers and other devices don't serve a purpose, but they are designed for specific purposes. Desktop computers remain the best all-rounders – and by far the most cost-effective and powerful way of using computer power and consuming "digital media" and services.
Furthermore, such devices are fashion fads as much as they are useful tools – many people seem to want an iPhone, ebook or tablet just for the sake of keeping up with friends, neighbours and colleagues (or, in the case of Amazon Kindles, to read filth on the train). When they lose their cachet, sales will no doubt fall.
Netbooks, for example, boomed in popularity in 2008 and 2009, before sales fell equally quickly as people moved on.
And desktop PCs, unlike the trendiest products today, don't need replacing outright when their batteries fail.