Unfortunately I don't have simple answers for you. I've seen about the same amount of memory usage for a simple application, with the usage being higher on Mac and on Windows. However, because of the way that Windows and OS X report memory usage, I don't think it's a fair comparison.
I don't understand the difference between Windows 32 and 64 bit. I'm surprised it's like that, I would have guessed the reverse if anything. You might want to add a bug on this over at bugbase.adobe.com.
I also suspect that you see differences between profiler and task manager because of the differences of what they are measuring. I'm not an expert on the profiler, I would suggest reposting this question over on the Flash Builder forum to see what they suggest.
I'm also surprised about the Mac vs Win captive runtime sizes. At first I assumed this was just universal binary bloat, but AIR 2.x and above are Intel only so that shouldn't be the case. Again, if this is an issue with you I'd suggest opening another bug at bugbase.adobe.com.
One thing we want to make sure of is that these findings haven't changed significantly from build to build. If you have found that previous versions of AIR used less memory, we'd want to know that right away so we could investigate.
Sorry for the delayed response. Thanks for your reply on this one. I will open up a bug in the bugbase. I have seen the difference in the memory consumption on the different bit OS and also the sizes of the bundles on windows and mac.