As you can see in the examples, bridge will not display transparencies in .ai files unless it is rasterized. I have white vector .ai files that will only show up as a white box. I can save it as an .eps vector and it will display correctly, but I want to use .ai files.
Here is something interesting, that I'd like to add. If you save as Illustrator 8, It corrects the problem, but who knows what problems it may cause.