I think that the intuitive thing is to expect that if you have, for example, Firefox at the left half of your screen, Kontact at the right, Konsole in the midle and other 6 apps here and there, the taskbar reflects their horizontal positions, not their opening order. Neither is very intuitive that you have to run your eyes over the taskbar to identify and localize the app you are looking for because you don't usually remember which program you opened first, and second, and third and...
As almost everything in KDE it should be configurable, of course. Maybe many users weren't interested at all in this behavior.