Why is this still version 3.0?

The 3.2-series of GlusterFS was probably not ready in time for Ubuntu 11.04's release. GlusterFS 3.2.1 will be in Ubuntu 11.10 (see https://launchpad.net/ubuntu/+source/glusterfs).

As for why Ubuntu 11.04 *still* uses GlusterFS 3.0, this is because software is not upgraded within a stable release, except to fix security bugs and serious stability or usability problems. See https://wiki.ubuntu.com/StableReleaseUpdates for details. If you want to use GlusterFS 2.3 in Ubuntu 11.04, you may want to request that it be available in the backports repository. Backports repositories provide newer versions of software, with new features, to existing stable releases. See https://help.ubuntu.com/community/UbuntuBackports for details and instructions for requesting backporting.

Other options for installing GlusterFS 3.2 in Ubuntu 11.04 (either instead of requesting backporting, or in the mean time before it is determined whether or not it will be backported and before the backport is ready) are to use the version from an unofficial PPA (https://launchpad.net/~semiosis/+archive/glusterfs-3.2) or (probably less preferable) to build from source yourself. (You could also attempt to use the version from Oneiric, but there is no real advantage of that over using the unofficial PPA, and a number of possible disadvantages.)