Nokia definitely went this way for a reason, though. It wasn't ineptitude or the fact that they didn't get it. They get it very well. In fact, they are making an effort to prioritize software services as part of a diversified revenue stream.
In the meantime, though, their primary business is making money by selling devices. It's likely that this will always be, at least substantially, the case. This is the case for SE, Motorola, Samsung, LG, etc. too, and as such they are direct competitors. If Nokia gave its competitors a store and maps and all that stuff for nothing, they'd be spending a ton of money to bolster the competition's position at great cost to themselves.
Proliferating the platform for everyone's benefit at your own cost is crazy. That's why Nokia bought out the part of Symbian that they didn't own and made it their own.
Let's be clear here, very few contributors to Symbian ever really contributed anything. Instead, Nokia went at it substantially alone and achieved some pretty impressive penetration. It's open now, but I really doubt it will ever gain traction outside of Nokia devices and I sincerely doubt any other vendors will ever make another Symbian device. Meanwhile, Nokia continues to improve Symbian for its own purposes.
Google, on the other hand, doesn't make money selling devices, they make money selling advertising and they expect that at some point they will be able to monetize Android. They are not competitors with SE, Motorola, etc., they are partners. As such they have a vested interest in delivering a platform that's as strong as possible to their partners so that it becomes as widely dispersed as possible. Of course, some time down the road, Google's partners are going to end up in a situation where Google's making all the money and they're doing nothing other than slim-margin beige-box hardware - that's a bad place to be.
Interestingly, most of Google's vendor partners know this so they go to great lengths to put customizations into their software. They are effectively contributing their resources to benefit someone else's (Google's) bottom line at their own cost. All they'll ever make are device profits.
There is no free lunch. Nokia refused to provide it, and although it seems like Google has decided to, in fact they don't either.