Xbox360:
made in japan with all japan made caps, fan bearings, etc., etc.; 1 single large fan at stock voltage +/- 3%.
increased clock speed for the GPU to 875 MHz
made the CPU cache run at full speed
made the VMX units double precision.
strip it of hardware texture compression
better trilinear filtering (same as G80, even though the 8800 GTX wasn't out)
made it so that 2 or 4x RGSS could be used in every game
32 bit fixed point z buffer and 32 bit fp z buffer formats only, stripped it of hardware stencil buffer.
stripped it of all RGB10A2 formats; color buffer could only be R16G16B16A16 floating point or linear.
double floating point precision, single (full) precision fixed point shaders.
wired controllers, 1khz rps, 4 controller ports; 4 USB ports can be used for Keyboard/mouse
GB ethernet port (I'm assuming it doesn't have one; I don't remember for sure).
display logic integrated into GPU die and capable of user adjustable input rates from 24Hz to 120 Hz.
built in HDD, exactly the same as my WD Black 500 GB.
integrated the northbridge and all other processors except the GPU into the CPU.
from a software point of view, no audio lossy formats allowed to be used; games would simply have to be downloads and/or on more discs.