Apple computer sales grow faster than PC sales for five years – but why? For the past 20 quarters, sales of Apple Macs – remember them? – have grown faster than the PC market, an analyst points out. But why do consumers, businesses and government want them?

What is Apple doing right in the PC market? And what, exactly, did it do wrong in the first quarter of 2006?

Those are the two questions that occur in looking at some of the numbers pushed out by Charles Wolf, an analyst at Needham. He’s posted an investment note on Apple which points out that Apple’s Mac shipments have grown faster than the PC market for the past 20 quarters (that’s five years in normal money).

OK, but what’s behind it? Why are all these home users, business users, government users getting Macs? One argument is that with Apple, you’re starting from a small base, so any increase is going to look dramatic. And yet something is going on. My analysis of Apple’s sales figures and the numbers from Gartner and IDC shows that in the second quarter of 2010, Apple hit 4% of the whole PC market for the first time in more than ten years; it hasn’t happened since 1998, and I can’t find the time before that when it was true.

In fact, my own analysis shows that if it hadn’t been for a stumble in the first quarter of 2006, that figure would be 26 quarters, going all the way back to the fourth calendar quarter of 2004, when Apple emerged from 10 straight quarters in which it grew less fast than the market – or in other words, its market share of all computers shipped shrank.

Yes, but why?

According to Wolf, “shipment growth has resulted solely from an outward shift in the demand curve rather than from a relative reduction in Mac prices.” We translate from analyst-ese: people aren’t buying them because they’re cheap, because (relatively) they’re not: you can get cheaper computers, as pretty much anyone knows, and as Microsoft harped on about with its “Laptop hunter” adverts in March 2009 – which, if you’ve forgotten, were about people trying to get value for money in buying a laptop. Much good those did, by the way – Apple’s share of the computer market, where three-quarters of its sales are laptops, kept growing from 3.35% to break through that 4% barrier.

OK, so what’s Wolf think is doing it?

“The key drivers of the growth in Mac shipments over the past five years have been the halo effects emanating from the iPod and iPhone,” Wolf says. “The Apple Stores have played an important supporting role in providing convenient destinations and support resources for Windows users new to the Mac.”

This is what has also been called “the halo effect”, where one Apple product purchase leads on to others.

And he thinks that will get bigger: “The iPhone is competing in the mobile phone market, one measured in billions of units rather than the portable music player market, one measured in millions of units. Of course, the iPad is waiting in the wings.”

You might have thought that the iPad had already been quite busy, having been on sale for more than a year, but perhaps not.

Is it that simple, though? It seems odd if the “halo effect” from iPhones and iPods is feeding through to business and government sales as well – the latter is notoriously indifferent to those outside trivia.

One argument is that the increase in Mac sales (in the last quarter, at just under 5m, a level it has been nudging for the past three quarters) is due to governments and businesses getting interested in developing apps for those iPhones, so they’re buying one to be able to run the iPhone Software Development Kit. And home users? Quite probably they are the ones who are trading up (or as Wolf puts it, exerting an outward shift in the demand curve).