Reminds me of when Stagecoach used to offer free buses to drive the competition out of business.
Well, not quite. Microsoft aren't doing it to drive competition out, they're doing it to survive. Everyone is trying for a complete ecosystem where everything just works. Apple are closest, but they don't do consoles and their hipster premium costs them customers. Microsoft's opportunity comes from the fact they cater for everything, phones, tablets, netbooks, laptops, desktops, consoles. They will be looking nervously over their shoulder at the open-source Linux crowd, Android/ChromeOS on phones, tablets and netbooks, SteamOS on PC-based consoles and Linux on laptops and desktops. If those guys ever get their heads together properly, maybe throw in Sony as well, then Microsoft are really in the shit. It's only really gaming that keeps me running Windows on my PC and Steam are really pushing for developers to make Linux ports of their games. If that becomes widespread, then bye bye Microsoft as anything but a business software developer in the future. They simply have to have their OS running on everything, then try and make their money through the app store or wherever else.
The way the world economy has gone, with recession and growing inequality, means it's the increasingly barren middle ground that has been twatted. Look at games developers, the triple A ones are still raking in the cash, like Rockstar, Activision and Ubisoft. The indies are thriving due to lower overheads so lower prices. The middle ground developers, with their premium overheads and indie quality are going to the wall. Doubtless other industries are finding the same thing, the auto industry for one with the likes of Ford and GM struggling. It's this kind of middle ground that Microsoft are trying to live in. This 'giveaway' may be their last throw of the dice. However, due to their fundamental corporate stupidity and greed as witnessed with the Windows 8/Xbone debacles I'd expect this to play out like the "Scorpion and the Frog/Farmer and the Snake" fables.
Saying all that, I've tried the Windows 10 preview and it's looking pretty good. However, I'd expect the 'free' upgrade to be the most basic version of 10 they can get away with which you won't be able to roll back easily. The functionality you're used to will come at a price, you'll have to pay for plug-ins to get stuff like multi monitor support, media players, disk burning etc back again because they know many people will pay to save pissing about looking for free alternatives. Just a guess, like.