First and foremost Linux for ARM has been around for years
http://www.arm.com/community/software-e ... /linux.php
Secondly Android was the first Linux for ARMv6
http://forum.xda-developers.com/showthr ... ?t=1596800
Actually Raspbian developers take Debian 7 "wheezy" Testing which is an official Debian Distribution for ARMv7 architecture and compile to work on the ARMv6 Architecture.
http://www.debian.org/ports/arm this is the older ARMEL Soft Float version.
http://wiki.debian.org/ArmHardFloatPort this is the newer ARMHF version.
http://www.raspbian.org
"The initial build of over 35,000 Raspbian packages, optimized for best performance on the Raspberry Pi, was completed in June of 2012."
The RPF offer Raspbian "wheezy" which is their version of Raspbian.
It should be noted that many software packages are available across all flavours of Linux, x86 / x86-64 / ARM / Sparc etal and even Unix