Maybe they will use it on more models. They have to start somewhere. Until recently, they had a corporate position that WP was better, no doubt influenced by the 100s of millions of euros Microsoft were giving them.
Why do you think Nokia have adopted Android for cheap phones? Will this decision survive the Microsoft takeover?
Btw, in case you have forgotten it, we concluded in another thread that Android was more efficient than WP in terms of memory usage, as 512MB Android phones are much less limited in terms of the apps they can run.
My friend, there's a HUGE difference between being able to run something, and being able to run it well...
Hence why Apple and Microsoft limit features in many ways. They sacrifice universal compatibility, in exchange for a much better user experience.
I.E: Apple's frequent decision to give older devices iOS updates, but to limit or completely rip out headline features on said older devices. Why? Well, even though the older updates probably could run all the features, there's a good chance they wouldn't do an ideal job, frustrating to user. It's an interesting choice, but one I agree with. Better to just not let the customer not even touch the feature, rather than them using it and face constant frustration. After all, you can't miss what you never had, so if they never get the feature, they can't really miss it. But if they did get it, then they'd constantly be getting annoyed when it didn't work ideally, constantly renewing frustration, whereas the complete absence of it leads the consumer to forget.
So Microsoft and Apple are simply cutting features for the sake of improving the user experience and reducing headaches for users. Sure, Android /can/ run lots more apps on a 512MB device than a 520, but let's face it: in most cases, the 520 will outperform the comparable Android.
Just like Windows Vista. Sure, plenty of devices could /run/ Windows Vista, but all except the most powerful of machines could run it /well/. Everyone else had to suffer through a slow OS that completely lacked any decent compatibility with Windows XP. Android is basically the Vista of the mobile world: very resource intensive. Low written requirements, but still very demanding in practice, with fragmentation galore.
Granted, things could be much better with Kit-Kat, but seeing as Kit-Kat is only really being found only on the most recent of flagships, we might not know how low-end devices handle it for a time (with the exceptions of those who like to flash their devices).
TL;DR: Sure Android can /run/ on 512 and even 256MB devices, but a comparable Windows Phone handset will likely perform much better, because running and running /well/ are very different.