We're talking about CS4 here: Flash was basically THE way to build UI back then. I wouldn't be surprised if it was one of the motivating factors for Adobe buying out Macromedia (aside from just quashing potential competition from Macromedia Studio).
Hell, a lot of high-budget video games around the same time used a little thing called Autodesk Scaleform. That's basically Autodesk's reimplementation of Flash Player (Adobe was too short-sighted to pursue this market) which game developers could quite easily license and embed into their games.
The wonderful pseudo-3D HUD on tye Crysis franchise is made with Scaleform. It's deprecated, and AFAIK, CryEngine doesn't use it anymore, but it made the best GUIs back then.
THE way to build a UI that worked and looked consistently across platforms at the time as well. It was a great time! Even now it still takes some work to achieve the same!
Hell, a lot of high-budget video games around the same time used a little thing called Autodesk Scaleform. That's basically Autodesk's reimplementation of Flash Player (Adobe was too short-sighted to pursue this market) which game developers could quite easily license and embed into their games.