Oops. My bad. Thanks all.
For what it may be worth to others:
Still wishing to avoid installing 209 additional library packages
(which is what the ia32-libs wants to fulfill dependencies), I found
that the following three -- well really four -- packages (in addition
to whatever was put in by the Pharo Debian package I already have from
the PPA) were enough to get the PBE image to pop up:
sudo apt-get install libuuid1:i386 libsm6:i386 libglu1-mesa:i386
(Installing libsm6 also installed libice6.)