> W czym KK góruje nad 4.2?
> Aby było jasne --- nie bronię A4.2, a jedynie pytam.

IMO przyzwoity Android to 4.3 i wyzsze.
W wielkim skrocie:

Android 4.3 Jelly Bean (API level 18) - pierwsza wersja z TRIM-em
Bluetooth low energy support
Filesystem write performance improvement by running fstrim command while
device is idle
...

Android 4.4 KitKat (API level 19) - ART, co prawda experimental
Android Runtime (ART) introduced as a new experimental application
runtime environment,
not enabled by default, as a replacement for the Dalvik virtual machine

Android 5.0-5.0.2 Lollipop (API level 21) - ART w pelni
Android Runtime (ART) with ahead-of-time (AOT) compilation and improved
garbage collection (GC),
replacing Dalvik that combines bytecode interpretation with trace-based
just-in-time (JIT) compilation

Android 5.0.2 - fix TRIM-a
Fixes a bug with TRIM support, which prevented devices from the nightly
on-charger cleanups of file system allocations if the device was turned off
while being charged, or if it was charged during the day

http://en.wikipedia.org/wiki/Android_version_history