I kind of wonder about this behavior as well.
Before, I opened the dmg containing the app, pressed the "blue pill" in the top right corner of the window to reveal the side bar and then dragged the app to the app folder.
In Lion, the blue pill is gone along with the menu choice and keyboard shortcut to show the side bar (at least from a dmg window), meaning that if the app dev didn't include a short cut to the app folder, installing apps just got a bit awkward compared to pre-Lion OS X.
I know I could just place the app folder in the dock and be done with it but I find this gui "simplification" (if that is indeed what Apple intened) odd.
What is the real intention here? To press app devs to include a convenient app folder short cut? That's kind of hit and miss right now. Or tin-foil-hat-scenario of pressing devs towards releasing on the app store, rather than selling independently?
There are quite a few smaller gui changes in Lion I just don't see the motivation for.