Don't think of this as an Android phone, it will never be marketed that way.
Think of it as a new operating system than just so happens to be easy enough to have Android apps ported to it.
If the changes to support maps, in-app billing and the Nokia store are as simple as Nokia makes out to be - then it's a bit of a no brainer for developers to do. Especially since it's far less effort than building a new app for a whole new platform (like, say, Tizen).
Finally, yes, Nokia could have just shoved out a pure Android phone with decent hardware - but, against the mighty Samsung's advertising budget and the fact that all the other OEMs are unable to turn a profile - how exactly do people think that Nokia will make enough money?
Not to mention that Nokia would be beholden to Google and where Google wants to take Android, which may not be in their best interests. It's a gutsy move, but if they didn't do something radically different then there is an extremely good chance that they'd just be another Android OEM making a loss.
Even the highly praised Moto X had a price cut in January - an immediate indication that it's not selling as well as hoped.