I would think this would hurt their overall adoption rates (especially long term) as people get sick of constantly upgrading their OS and dealing with any fallout that results.Apple's willingness to obsolete their old tech has been the plan for a long time, and works fine for them and the higher-spending niche they're targeting. Basically the pitch (to oversimplify) is: we will make technical decisions based only on supporting the last two or three years of customers. If you keep up with us, things will work great for you, because we won't be slowing things down to maintain compatibility. If you have hardware or software older than that, good luck, but it's not our problem if our new stuff doesn't work for you. The only promise is that we won't compromise the product in order to save you money.[1]
This works for Apple (and the customers who keep upgrading) because it's nice to live in an ecosystem where you can assume modern hardware and software -- for example, where developers can reasonably target multitouch trackpads or webcams or motion-graphic APIs or whatever within a year or two after they're released, and cruft can be thrown out of the OS when it's no longer needed.
As it happens, I'm one of those customers -- I spend more than half my waking life on computers, and I don't mind spending a little more to work with modern hardware, and to have an OS that assumes I have modern hardware. I'm not trying to glorify or demonize that -- it's just a business model targeted at a certain part of the market that likes it that way, or at least accepts the downsides in exchange for the upsides.
[1] Please don't feel compelled on my account to recite all the ways Apple doesn't live up to this pitch. Believe me, I know. (Quicktime 7?) I still think it's a decent approximation.