The problem with PCLinuxOS is that by default it uses KDE 4 *yawn* instead of GNOME, with its ease of use. (Of course, it also has GNOME as a secondary option, but on a different CD). Ubuntu, even though it uses a different visual appearance/shell interface
, is GNOME at the core. That means all the GNOME apps you know and love are built right in.
What it really comes down to is Qt vs. GTK+: While Qt has a proprietary variant (even if the proprietary variant is basically identical to the open source version, it still can be used to develop proprietary apps), *all* of GTK is open source.