I by far an expert on the subject but I think you're missing the point slightly.
Running having 32bit apps run fine under 64bit is not the issue. Because a 64bit OS is optimised for 64bit addressing. So when it has to run under 32bit compatibility mode it's doing a lot of extra work under the hood to get this right. Granted if this performance drag is not noticeable, then what the problem? Well a couple of things come to mind. Firstly it's one of those things that "just isn't right" and gets a decent amount of people upset. Secondly is a blatant abuse of the processing power you have available. What about lower power machines (netbooks etc) where you could possibly notice this? How much of a drag this actually is, I'm not sure....
The whole deal is also not really about assigning large amounts of memory to a single process. Granted there are situations where you would benifit from this. SQL server and gaming are two that come to mind, it's about total system memory, which means less swapping and better performance.
I still maintain my first point, which is until there is an economic reason for software vendors to support native 64bit, we wont see widespread adoption. As for those guys who's software just doesn't work in a 64bit environment, they are the ones who deserve the linching.
I totally get the "just not right" effect. Like I said, it's not the optimal solution. Getting companies that have no financial incentive to re-release their software in 64-bit form is the main problem.
For MS to get people to migrate to 64-bit, they have to get many of these old 32-bit programs running in a 64-bit environment. They can't force the vendors to do this, and they cannot do it themselves, as this is not OSS, and there's a LOT of 'custom' software out there.
For the major software that DOES gain from 64-bit addressing, you will find 64-bit editions.
A browser, and a flash player is not something that really gains from 64-bit addressing, and for that the Windows 'interim' solution is excellent.
As soon as you squash PC with your 32-bit emulated browser, I'd say a 64-bit version becomes important, but until that day it's a want, not a need.