I am sure they will do this one day, but they're still building up all of those extra ingredients needed to do so. Google Play is a good move towards this, and if they can also progress things like Google Wallet and improve other services still in beta, they can take the plunge.
Do so too early and they'll just screw it all up and go back to square one!
Google doesn't advertise much, but they did spend a small fortune pushing the Chrome browser. Not sure why they did that, but a lot of people are now using Chrome (on PC and Mac) so they can do it!
They have had plenty of time to get their sh*t together! Android has been around as long as the iPhone has. Why is Apple so much further ahead in terms of their App store and dominate marketing? Android has literally HUNDREDS of devices to market to people, Apple has like 3. Just another example of how clueless Google really are about this whole thing. They license Android out to companies looking to make a quick buck that make crap products no one buys, there are like 5 different version of Android being run, they can't seem to organize the Market and they can't even get a campaign together. The general public only knows Android as a Droid, you know, the phone Verizon spent millions marketing that actually got the name out. Mention another Android device to someone and you will get a blank stare. Google just doesn't seem nearly as dedicated to Android as Apple does to their OS and devices.