Yep, Apple has both Microsoft and Linux nipping at its heels.
Due to potential or real patent wars, however, I doubt Apple will die. I could well see Apple promoting a parallel Linux product, on the philosophy of if you can’t beat them, join them.
Despite this bitching by lovers of other companies, it turns out those companies are following Apple: phones without SD card slots or removable batteries for example, and downloads from that company's store. You can't make devices this small with this much power and still make them easily hackable.
And despite this bitching, Apple still commands the #1 consumer satisfaction spot for the latest in eight consecutive years, far ahead of the nearest competitor. Apple makes their customers happy. Those customers buy more Apple products, and tell their friends how happy they are with the products. That is why they won't fail.
A friend asked me to go with him to Best Buy to replace his dead PC the other day. I thought a switch to Mac would be a stretch for him, so he'd probably be more comfortable sticking with a PC. He has never owned an Apple product. I took him straight to the mid-range PCs and explained what could be a good replacement. He decided the all-in-one configuration was best for him (he wants simple, but doesn't want a laptop), but he was worried about their construction. So I took him by the iMacs to show him a reference point for solid construction (the rest are cheap plastic) and started to take him back to the PCs to pick one.
Too late. He was hooked, I couldn't drag him back to the PCs. Instantly, the quality did it, he felt all the others were cheaply made and had dull screens. Ten minutes playing with it and he was comfortable enough with the OS to buy one, regardless of only having ever used Windows. He spent more than he'd planned, and I kept mentioning that was a lot of money, but he felt it was well worth it. After all, that's how much his PC had cost him in 2005.
Quality: Another reason why Apple pushes so much product.