You aren't the only one saying it might be free. Can you provide a precedent? When has Apple ever offered a free OS or major software (aside from the ones installed on the machine)? How would they make money with all that product development?
tl;dr: The Mac is now just a device. Apple doesn't charge for major OS releases on their devices.
Long version:
There doesn't have to be a precedent. Consider Steve Jobs' statement at 2011 WWDC that Apple is going to, "...demote the PC and the Mac to just be a device; just like an iPhone, an iPad, and an iPod touch." With today's announcements, Apple has truly made the Mac just another device in 10.8 and Apple doesn't charge for OS releases to their devices. Why would the Mac be any different than the others? It's now just another device. The move to a yearly release schedule all but proves this, in my mind. They want to keep both OSes in sync so that the user experiences can be unified in an iCloud way.
Surprisingly, $29 is a barrier to updating for some users. It's far better than $129, but it's not $0. Unless users upgrade quickly to new OS X releases, Apple won't be able to continue pushing their iCloud strategy on all of their devices. Removing the cost barrier is one way of ensuring more people upgrade sooner and this is better for Apple in the long run due to the better experience for customers.
Apple's amazing bottom line comes from the purchase of high-margin hardware products, not from OS software releases. If Apple is willing to forgo revenue from iOS releases (which can't be significantly cheaper to develop and test than OS X), then I see no reason why they won't eventually do the same for OS X since the Mac is now, say it with me, just another device.
Perhaps I'm wrong, but this all seems way too logical to me. I will be shocked if Apple doesn't take this approach going forward. It makes too much sense.
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I'm not sure I understand you, I am on Lion, when I click and hold on an application icon in the dock, all the open windows of that application are listed on the top of the pop up menu. I use this all the time when web browsing as I will often have multiple windows instead of tabs for this exact use.
That's different. The OP was talking about Dock Expose, now called App Expose, where just the open windows for the app will show. What you see is just text, not the actual window contents (which is far more usable). Read my response a few pages back.