Microsoft was for many years but as of earlier this year, Apple's market capitalization hit 683 billion as compared to Microsoft's current value of 338 billion dollars. So, now after all the years of Microsoft's popularity, Apple has taken over the market.
Apple had a fun system to use and their icons made it very simple. But they were EXPENSIVE.
So Microsoft grew fat on an inferior system. (A joke doing the rounds in the 1980s was, "Where can you find a user-friendly program that will still respect you in the morning?")
Then came Windows and the multi-billion dollar court case between Apple and Microsoft. Microsoft won and Windows revolutionised the way we do things. Apple now had little to offer that Microsoft couldn't do as well, and the price difference remained.
Over the past few years Apple have improved their marketing techniques, lowered their prices somewhat, and are once again competitive. The figures shown in Rooster's post show that they have not only taken the lead but may become the dominant player.
Certainly when Microsoft begin charging their planned annual rental for Windows and Office (instead of selling them without restriction) Apple are likely to receive another boost. I might even make the switch myself.
Apple's original computer almost broke them, as it was pushed as a personal computer, but was not IBM compatible. They then developed the Mac, which was aimed at business. (I found it great as a business computer, much easier than the IBM compatible computers). As more people used the Mac, it became more popular. Especially after they invented the program for music. The price went down, and it flourished, but it is only in the past few years that it has caught up with Microsoft.
Microsoft got ahead because it was cheaper, and almost everyone wanted to say they were IBM compatible.