Not sure where you searched but it has been posted at TS I'm pretty sure.
As for why they did it, the theory (since that's really all we have to go on) is that it is to help avoid people from doing things they shouldn't. The theory has many doubters since it is no problem to view the System/Library which many would consider slightly more dangerous?
OTOH, I have noticed that my normal method of archiving before making updates is slightly different in Lion. While the menu commands for duplicating or archiving an item in the System seem to be working, it took me a few tries before I noticed that the duplicates were actually being placed on my Desktop.