A-ha!

You actually have to do work to run 32-bit binaries on 64-bit linux. I knew this, but I rediscovered this fact this morning.

Of course, this got much harder in modern Ubuntu:

sudo apt-get install libxtst6:i386 libXext6:i386 libxi6:i386 libncurses5:i386 libxt6:i386 libxpm4:i386 libxmu6:i386 libxp6:i386
sudo apt-get install libstdc++6-4.8-dbg:i386

Sigh.