"ART: ... Truly cross platform: ARM, x86, MIPS"
Sounds like they may be setting up to make a proper run at the desktop market? Now that all these Windows 8 machines are out there with cheap touch panels, it's shown that cheap desktop/laptop computers can exist with the necessary interface bits to work.
edit:and watches and cars apparently
Dalvik, and Dalvik's JIT compiler are definitely tuned for small batteries.
The Dalvik JIT compiler focuses on critical sections of code. There's a reason you don't see Hotspot on battery powered devices.
Large amounts of the Android framework, especially the foundations of drawing and the View hierarchy, are in C or C++. Compiling an interactive app to native code makes much less difference in performance than a synthetic benchmark of DEX interpretation might lead one to think.
Hotspot get its name from the term of art for a critical section of code, though. That's not something that makes them different from each other; it's what they have in common.
What separates them must be that only one of them was designed with a power budget in mind.