Every player in the smartphone field wants to differentiate, and nokia till now has had the luxury of owning or controlling at least 2 or 3 platforms, because controlling a platform gives you a totally different kind of leverage as opposed to being a 'me too' player and competing with all the other players on their terms.
The trouble is that the whole phone market paradigm has changed, from one where you sold phones and got margins on the hardware, to one where the hardware margins have shrunk, and in either case, hardware is a much tougher market to compete with all the huawei's and micromaxes of the world. So what do you do? From selling a product which is becoming increasingly commoditized, you move to more of a service player than a product player, because its harder for your competitors to copy your service aspect.
That is what apple has managed to do successively earning record profits, both on phones and laptops, while the hp's and dells of the world are figuring out what happened. You are competing at a different level. And at that point, your product sales become just one of your revenue streams, and you look at others. Take Apple and Google, two of the most sucessful smartphone platform owners. Google monetizes the android platform by harnessing the data it collects and finding more meaningful ways to target customers, and sell that data to advertisers. Apple uses it to lock users to its ecosystem and buy more of their products and their ecommerce platforms.
That's the problem where Microsoft is having a hard time, and HP lost, and why I predict canonical will have a hard time, because their plan stops at selling the phone. Microsoft is banking on the UI commonality between WP8 and Windows 8, and the common ecosystem. HP put webOS into everything they had. Printers, and sadly not much else. Wasnt enough to lock customers, and their bungee CEO also didnt do any help either.
Nokia wants full control - the platform, the hardware, and the carriers too (which is why it's prescence in the US isn't as big as it should be). It's taken an all or nothing strategy. Lets see if their bet pays off.