The meaninglessness of "HD Twin" term, predictions & prize for being right.

[Procrastinato]

Both have 512MB memory. Both have similar (in performance) CPUs and GPUs. Crossplat development between these two machines is arguably easier than any other two consoles in history.

The Wii is a standout, architecture-wise.  Hence its not included, and the other two get the "twins" moniker.