I think you have few facts wrong.
Windows Phone been running on ARM since it's release. Even Windows Mobile ran on ARM chips from mid 2000's. In fact, Windows Phone never ran on Intel chips. Even original Windows CE stuck to ARM, and another architecture, the name of which evades me right now.
.NET is just a runtime. It's not as memory hungry as people make it out to be. It's all about how developer codes the program.
.NET is slow if you are running it on ancient hardware. I am talking Pentium 4 - era Celeron chips, and 512mb of RAM. Any PC you buy in a store today won't have any issues with .net.
Since .NET is just a runtime, it has no effect on battery. You can have a developer code a program that may use up a lot of resources, but same can be done in Objective C, Java, etc.
While a lot of Windows applications require .Net, core Windows does not. And what destroyed Vista was not .Net, but a very rushed release. While service packs later made Vista a great OS to run, the damage in public's view was done, and Microsoft quickly locked it up in the same cage with Windows ME.
Android can and always could (well, starting at Android 1.5) run C and C++ code natively. Source:
http://developer.android.com/tools/sdk/ndk/index.html
I wouldn't call original xbox a failure. It was a very cheap PC. Very moddable, and very flexible. The heart of it was a Celeron 700-ish mhz chip, which was quickly put to use by homebrew developers. And it was the first console with a hard drive. Sony's hard drive kit for PS2 does not count. At it's generation, it had great graphics, and I believe it was the first console with proper online capabilities. In fact, there was no other console Microsoft could copy. By then, PS1 was outdated. When PS2 was released, xbox development was already very close to completion. Nintendo didn't really have much out there. Gamecube hit US in 2002, while Xbox was released in 2001. If anyone "stole" anything, it would be Sony, for their online functions in PS3.
How's xbox 360 a failure? It's still going strong. Kinect is wonderful. Media integration is years beyond PS3. It's not just a console, it's a great family entertainment device, media center, streaming "receiver". Every major game (save for exclusives) is released for 360 and PS3. If anything is a failure in current console generation is Nintendo Wii. While a great idea, it quickly fell behind.