Actually, they have invested in previous versions of Windows. Businesses are the last ones who will be rushing out to get Windows 8 as most are now just embracing Windows 7 and migrating to it from XP. They wont be considering Windows 8 for a few more years so it wont be on their radar. So the biggest market will be consumers and that is where the potential for slow adoption comes. If they dont like it, if they cant see past their ipads and the like.
Anyway, I'm not saying it will fail, just expressing my disagreement with MS tying everything to Windows 8's launch when they could use the phone more aggressively now as a teaser of things to come.
That's why I said that the worst that will happen is SLOW adoption.
There are still many businesses that do upgrade. And since Windows 8 still has the desktop available, the types of businesses that were early adopters of Windows 7 will also be the same ones that will be early adopters of Windows 8.
Sure, the giant businesses, may be slow to adopt. But they've always been that way. It's not like they'll be slower with Windows 8 just because it's Windows 8. Like any version of Windows, they'll wait for the bugs to be worked out first.
The fact that Windows 8 will be available on Tablets will be a big plug for MS. And the fact that there will be strong integration between different MS products will help MS keep a large part of the consumer market.
Even if Apple does gain some market share, MS will still own a HUGE portion of the market. So when anyone worries about failure (not you), then I see it as unjustified panic.