Instead, what if Apple distributes 10.6—assuming there is a 10.6, as described above—as a free update to anyone running 10.5 on an Intel-powered Mac? Sure, we’ve become trained to expect a $129 upgrade fee with each major change in OS X’s version number. But this wouldn’t mark the first time the company released a major OS X update for free: OS X 10.1 was a free update, too, for all those who dove in with 10.0.
So why would Apple give this rumored update away for free? If there really aren’t any compelling new core OS-level features, I don’t think Apple would find a lot of buyers willing to pony up $129 for 10.6, even if it were faster. Although Leopard may have some issues, a compelling sense of overall slowness is not one of those issues. And clearly nobody is going to pay $129 for improved stability and security—again, OS X 10.5 doesn’t have stability issues for most users, and the platform is still yet to be affected by any large-scale virus or malware infestations. So if Apple can’t make any money on this—in fact, it will cost the company money—then why do it?
The answer, to me anyway, is resources. Right now, Apple has to extend its OS X efforts to include hardware that isn’t getting any younger—in addition to supporting new Intel machines, it also must make sure to support PowerPC processors. If Apple were to continue on its same dual-platform approach for a theoretical OS X 10.6 update, this would mean another 12 to 18 months of work supporting both platforms. (Remember, Leopard finally made it to market two-and-a-half years after Tiger.) But if the company instead released an Intel-only OS X 10.6 update very soon, that would clearly tell everyone that the next major update to OS X would also be Intel-only. So the company can then work on a full-blown Intel-only OS X 10.7 release, making OS X 10.5 the last release for PowerPC Macs.
By not including any low-level changes in OS X 10.6, Apple also would appease its developers, some of whom are just now finishing their migration to OS X 10.5—the developers would probably not be very happy next week if they were told that their code needed to be updated yet again. Similarly, PowerPC users wouldn’t instantly be left out in the cold—they probably wouldn’t soon face “10.6 only” releases from their favorite vendors under this scenario, as anything that ran on 10.6 would also run on 10.5. By delivering a feature-limited free update for all Intel Mac users in the near term, Apple would free up its resources, developers wouldn’t be forced to revise their code again, and OS X 10.5 PowerPC users wouldn’t need to fear a short-term abandonment.
http://www.macworld.com/article/133787/2008/06/osx106.html