I have installed two versions of Ubuntu 13.04, the 32-bit and the 64-bit. Both are fully updated. The 32-bit one has a strange problem: the Software Center doesn't show all available packages. In the 64-bit version, I can search for
libsdl for example and it shows up. In the 32-bit version, there are never any results. Many packages from the standard repositories ("universe", I think) never show up.
In System Settings, the preferences for Software & Updates are identical in both installations (and the "Independent" checkbox in the "Other Software" tab is checked.) In addition the
/etc/apt/sources.list files are identical in both installations and there are active entries for "universe" and "multiverse".
I should also mention that these are fresh installs and I haven't tweaked or changed anything. So why doesn't the 32-bit installation display the packages?