This guy has it right. These days, if you're putting more than 4GB of RAM into a computer, I'm sure you're running a processor that supports 64-bit Windows. Personally, I feel that companies producing software that is not 64-bit compatible are being lazy and irresponsible. They're negatively affecting the software industry by requiring other developers to produce both 32- and 64-bit versions of their software since both systems are still supported. How much of that developement time and spending could be redirected to improvements to other areas or eliminated and passed on to consumer or stockholders as increased profit margins?
The 4GB RAM limit is a smart move by Microsoft to push computing towards 64-bit. Basically, if any software company wants their product to run on a system with more than 4GB of physical memory, they'll have to start supporting 64-bit Windows. Perhaps it's not about the money. Perhaps it's a political move to push progress.
Disclaimer: I don't care about backwards compatibility, and I look down on anyone who uses legacy software as a lesser person.