Why are people talking about resolution on the rMBP? The unit is ALWAYS running at 2880x1800 regardless of the setting used. The scaled "resolutions" are simply rendering the GUI larger to be more visible. Setting it at larger scale does NOT change the resolution at all! NOW...that being said....3rd party applications with low res GUI elements will look worse because they are being zoomed in on in order to accommodate the scaling.
thats only the normal desktop settings. Fullscreen games and such can adjust the true resolution, as well as 3rd party apps that can adjust the true resolution... so no you are not always stuck in 2880x1800 with a scaled desktop, thats just Apples default and what options they give you in Display System Preferences.