MacOS – HiDPI on Lion: Most windows blurry

In order to make an app I'm developing Retina compatible, I enabled the "HiDPI" mode on my Mac (OS X 10.7.4 Lion), since I don't have a Retina MBP. The Quartz Developer Tool worked as indended, and I can select the HiDPI modes in system preferences. However, almost everything is rendered in scaled mode, i.e. pixelated. Only some parts of the "shell" are rendered with sharp fonts; the menu bar, the dock, Launchpad and Mission Control, and the "About this Mac" window. Everything else looks bad, including the app I intended to fix.

I remember this used to work, at least for a couple of applications (and my own, if I edited the Info.plist file accordingly). Is something broken on my system, or did maybe an update remove this feature for non-retina-MBP Macs?

The screenshot doesn't really do it justice. You can see the effect better if you view it in another tab. Also note that while the Firefox version shown might not have Retina support (I don't know), this happens with every other app on the system.

Compare the window controls and fonts, between background and foreground windows (and please excuse the German text :-)).