This is said repeatedly on this forum when the subject come up, as if Apple only needs to flip a switch to produce a something that is better than Photoshop, InDesign, Illustrator, Fireworks, etc. It is not like that, if it were so easy there would be a plethora of alternatives on the market. Look at people like Corel and Quark who have been making their products for decades and both have given way to Adobe's own offerings, specially Quark which was the dominant product. Adobe has been working on their products for decades, there is a lot of experience on that which isn't improvised with the mere thought of "let's build a Photoshop killer".
Re: Quark -> InDesign, here's my experience. In '04 we upgraded the studio I worked at, and went all OS X (Panther, at the time). Like many agencies, we upgraded all our software, so moved from Quark 4 to 6 and bumped all machines to Adobe CS1.
Quark 6 was a mess. We paid a small fortune for it (because it was OS X compatible) and it didn't work correctly. Especially bad was the point where it wouldn't save files. Their helpdesk in Europe was rude and unhelpful. Eventually they told us to downgrade from 6.1 to 6.0 and sent us a CD with the software on it... only they sent us yet another copy of 6.1.
InDesign was mature enough to try, and didn't cost anything since it was included in CS. We had taken advantage of the upgrade offer and upgraded from any version of Photoshop to the entire CS suite for the same price... even an old PS 2.5 on floppy disk. We had nothing to lose.
About a month later, everyone was fine in InDesign. Many had used PageMaker years before and adapted quickly. A couple of hardcore Quark users struggled because they were used to using mainly keyboard shortcuts and didn't really want to use new software, but even they, 6 months later, had settled down.
To answer your point about 'just make a Photoshop clone', well it's possible.
Consider this: Apple buy Pixelmator. Apple throw extra resources at it and add the things PS users need (like, say, CMYK support). They spend the next 5 years developing the software, getting it up to scratch. Perhaps they integrate the good bits from Fireworks, too. Once it's suitable for 70% of the main Photoshop uses and 50% of what Fireworks does, they offer it dirt-cheap as an upgrade, say $30 for any PS, FW or CS suite user. Who wouldn't give it a chance? And it's only what Adobe did to make InDesign dominant.
In terms of replacing the CS (design) suite entirely, Apple need only produce a PS clone, an Illustrator clone and an InDesign clone. I'm sure they could afford to buy Quark (or produce their own page layout software). OS X already outputs PDFs so Acrobat need not be replaced. They have no need for Flash and can ignore it. There are many Dreamweaver replacements out there already. Why even build one when people can buy Coda (or whatever) for so little?
A final point: If MS bought Adobe, unlikely as it is, and stopped producing CS for the Mac... so what? In my experience, the last must-have upgrade for Creative Suite was CS2. There are no new features that the average digital studio needs in CS3, 4 or 5 that make it worth spending $700 per seat to upgrade.
The main reason any digital agency I know of has upgraded for is compatibility. When your printer moves to CS6, they will be able to open files from CS5 and 6 only. If you are still on CS4, it's time to upgrade. When I get sent a logo in an AI file from a designer for use on a website, my copy of CS3 may not open it if it's from CS5, and they can only save down to CS4. At that point, it's time to upgrade. Equally, if I need a new Mac but Snow Leopard won't run FW CS3, I need to get CS5.
If CS went PC-only, wouldn't that mean all Mac using creative types would just stick with the final version of CS available to them until something better came along? Unless enough of their clients and suppliers used PCs and the latest version of CS, how would they be affected? Hell, make CS6 the final Mac version. So long as Apple can keep their OS running it, no-one would care.
Looking at what small teams gave been able to create for the Mac (Coda and Pixelmator being good examples) in the last few years, I can only imagine what would happen if they were bought by Apple and allowed to double their resources.
Quark thought they were untouchable, especially since they were so entrenched in the the publishing industry, but it only took 5 years for they to lose their position.
