Comment 1 for bug 1198490

The "64-bit version" is actually a Multi-Arch package with dependencies on the 32-bit files. Please try running the following command:
dpkg --print-foreign-architectures
If it does not output "i386" then that means that Multi-Arch support is disabled. You can enable Multi-Arch by running:
sudo dpkg --add-architecture i386 && sudo apt-get update

I haven't actually heard of people having problems with a fresh install of 13.04 though, since Multi-Arch should be enabled by default in that one.