My understanding is that Google or Intel worked some SSE3 dependencies into Android-x86, despite absolutely zero support for SSE3 (or even SSE2) on the ARM cpus that make up 99% of android devices.
There has been some talk of removing said deps in a fork or as an optional patch, along with PAE (even Android X86 shipping devices only have 2G memory... WHY require PAE?)
Again, it's a matter of the relatively narrow hardware support... The Linux kernel supports many things, and Mesa also supports many video boards
but not everything is "on"in the builds.
My 4 & 5 year old Lenovo laptops work great on 4.3, intel graphics, intel core2duo CPUs and chipset.