I find that Qt apps also feel native on a wider variety of linux desktops than Gtk apps do. For example, Gtk (since v3 I think) encourages apps to override the window manager, stuffing widgets into the title bar and breaking actions like window shading/collapsing.
In general, Qt acknowledges the differences between desktop styles and tries to match them, while Gtk doesn't seem to care about any style or interaction model other than its own.
