AWOL:
Actually, they are quite correct.
The AVR "running" Linux is actually an ARM processor running under emulation on the AVR.
Regardless whether it's running an emulator or not, it's still running Linux on it's own h/w.
An emulator is only a translator of sorts after all.
Besides, the question was about the DUE, which has an ARMv7 core. Linux has and does run on the Cortex-M3.
The real issue is the lack of RAM, but the DUE can support external RAM no problem.
Like I said initially, it can be done, but it's probably not worth it.