The current Mac renaissance has a certain “be careful what you wish for—you just might get it” feel to it. After more than a decade of stagnant market share, the Mac is thriving.

Apple used to sell about 1 million Macs every fiscal quarter. Now it sells three times that many, and it’s getting close to four. The longtime lament of the Mac enthusiast—Why don’t more people who are unhappy with Windows PCs switch to the Mac?—has been answered. They are switching, in droves. Quarter after quarter, Apple reports that over half of all Mac sales in the company’s retail stores are to first-time Mac buyers.

This sort of renaissance is rare. When markets are new, they tend to be fluid. But when they’re old, they’re settled—and a decade ago, the personal computer market seemed settled. But at some point about five years ago, that changed, and the Mac has seen year after year of consistent industry-leading growth.

Just what longtime Mac enthusiasts have always wanted, right?

Long-term doubt

The irony is that there’s more doubt today about the long-term prospects of the Mac than there has been at any time since Steve Jobs returned to Apple in 1997. Rather than suffering defeat at the hands of a competing platform—like, say, Microsoft Windows—the problem for the Mac today is that it has been overshadowed by its own sibling, the fabulously precocious iOS. There are more iOS users and developers than Mac ones. For all the remarkable growth in Mac sales (especially for a 25-year-old platform), after six months of life the iPad was already outselling the Mac.

Here’s the short version of the “Mac is doomed” scenario: iOS is the future, Mac OS X is the past, and Apple is strongly inclined to abandon the past in the name of the future.

You can’t really argue with that, can you? But the premise that the end is near for the Mac presupposes quite a bit about the near-term future of iOS.

Apple’s cultural aversion to legacy technology isn’t about a lack of seriousness, or a short companywide attention span. It’s not about being attracted only to the new and shiny. It’s about fear—the fear of being weighed down by excess baggage. Fear that old stuff will slow them down in their pursuit of creating brand-new stuff.

So it goes: Classic was abandoned as quickly as possible in the transition to Mac OS X. PowerPC support was dropped in Mac OS X 10.6 three years after the last PowerPC Macs were discontinued. The 64-bit Carbon application programming interface died. It’s not that these technologies were no longer useful. It’s that continuing to support them would have slowed the company down. Time spent supporting the old is time not spent building the new.

At typical companies, “legacy” technology is something you figure out how to carry forward. At Apple, legacy technology is something you figure out how to get rid of. The question isn’t whether iOS has a brighter future than the Mac. There is no doubt: it does. The question is whether the Mac has become “legacy.” Is the Mac slowing iOS down or in any way holding it back?

Heavy versus light

I say no. In fact, quite the opposite. For one thing, Mac OS X development has been slowed by the engineering resources Apple has shifted to iOS, not the other way around. Apple came right out and admitted as much, when Mac OS X 10.5 was delayed back in 2007. The company’s explanation: It had to shift key engineering resources to help the original iPhone ship on time.

The bigger reason, though, is that the existence and continuing growth of the Mac allows iOS to get away with doing less. The central conceit of the iPad is that it’s a portable computer that does less—and because it does less, what it does do, it does better, more simply, and more elegantly. Apple can only begin phasing out the Mac if and when iOS expands to allow us to do everything we can do on the Mac. It’s the heaviness of the Mac that allows iOS to remain light.

When I say that iOS has no baggage, that’s not because there is no baggage. It’s because the Mac is there to carry it. Long term—say, ten years out—well, all good things must come to an end. But in the short term, Mac OS X has an essential role in an iOS world: serving as the platform for complex, resource-intensive tasks.

The funny thing is, the best slogan to describe the Mac’s role is the same one it started with 25 years ago:

The computer for the rest of us.

[John Gruber is the author of Daring Fireball.]