Apple has been excelling at building great consumer devices, but has a terrible track record in the professional tool arena for the past twenty years, and I don't see this changing for several reasons:
-COST: While the PRO hardware is superb indeed, it cots a lot more than comparable platforms running Linux/Windows. Especially when you factor in the cost of keeping hardware up to date, and innovation cycles. Businesses are a lot more cost conscious than household consumers for tech stuff because they are running a business. No need to explain this.
-Software: I work in visual effects for film and TV. We arguably have some of the highest demands in terms of computing power. Also, we use a very diverse tool set. There are simply too many applications that do not perform well enough (for various reasons), or at all, on Mac OS. Because of this, and the cost of Apple hardware, the vast majority of studios run Windows/NIX platforms and use workstations that constantly get upgraded. Apple has made many attempts to make inroads in this industry, with a track record of failure to gain a foot hold. They bought Shake, the premium compositing software at the time, and attempted to draw people to buy Mac hardware in order to run Shake by doubling the license price of other platforms. This resulted in Shake being abandoned and paved the way for Nuke to gain supremacy. Shake development died off within a couple years. Then they bought Final Cut Pro, the gold standard of video editing platforms that nearly EVERYONE used. Today, Avid and Premiere hold the market. Apple effectively sank the most popular video editing tool in the world.
Apple's sandbox business model, where they want to control the software, hardware and all peripherals, creates huge lags in development cycles. They always manage to release a new Mac that seems to be superior to PC's for about 6months, and then PC's catch up and these expensive Macs are behind the curve for a couple years, until Apple refreshes the lineup. That's been the current track record. Now if this were to change, who knows. As it stands, businesses who need to watch their margins will probably look elsewhere, and this will leave PC's with the market lion's share.
The day of the Mac being the supreme multimedia creation platform are over. And that puts the viability of Mac Pro hardware in question. PC's have an embarrassment of choices for hardware and software better tailored to individual needs than you can find in the Apple world. GPU's are an essential part of the equation for high end workstations today. I'm not going to spend a premium for a mac "versioned" GPU built by a third party when I can get the same tool for less running Windows or Linux. Having a slick iPhone or tablet at home is one thing, but I really don't care what my workstation looks like. It's a tool and as long as it does the job well and doesn't cost me a fortune, that's all I ask for.
And for print work, or Audio work, a simple desktop PC can handle all this with ease these days. You can get Pro Tools on Windows just as well. Macs were popular when all that auxiliary hardware was clearly better on Mac OS, and easier to configure, but this is a thing of the past. Today, Mac Pros are beautiful, expensive beasts that do not bring much of a business proposition to the table. Apple would need to match its pricing to that of PC's in order to gain market share.