At least in XFCE, that "reasonable expectation" has been fulfilled for as long as I can remember.
In KDE, I have no idea, because the last KDE that I have used was 3.5, which was the best desktop environment that I have ever used, including in comparison any Windows or MacOS version (while KDE 4.0 was the worst).
I tried it again last year some time and it was neither as configurable nor as stable as 3.5. Granted, maybe it's just rose-coloured glasses, but Trinity DE still seems to provide a better experience for me to this day.
In KDE, I have no idea, because the last KDE that I have used was 3.5, which was the best desktop environment that I have ever used, including in comparison any Windows or MacOS version (while KDE 4.0 was the worst).