doubleofive said:

Here's the shot where it looks like a couple guys are trying to look out a window in the rebel control room:

Watch it in motion, the guy with the arrow is defiantly not looking at the glass, but leaning forward to look through it and down. The problem with putting a window there is the lighting, unless the window just happens to be in shadow in the outside shot.

The problem with putting a window there isn't just with the lighting but it is also part of the command centre that we see earlier on in the movie. So changing any part of the set would throw in a big continuity issue.