There is no reason for upgrade to win7 unless you like the Win7 GUI...
What is called 32 bit was in fact 36 bit since 1995 ( previous century !!! )... with PAE, limit of ram was around 64/128 gb ram... more that enough for any game... devs have never support it because desktop version of windows was limited to 4gb due to licensing and that only with server version of windows OS, it was possible to use the full power...
PAE incurs significant performance penalties on memory access, and isn't even remotely practical for games that need low-latency access to do anything well. It's also not used anymore on servers as 64 bit has replaced it (PAE was really just a hardware hack to get around the CPU not being able scale up past 32 bit). 64 bit is also a lot more then just more memory, the CPUs themselves have more registers and compilers can generate more efficient code for them.
Click here to see the limit of all windows OS, 32 bit and 64 bit version... funny to see that a windows 2000 datacenter 32 bit is able to address more memory that the brand new win 7 x-64 Home basic & Home premium version !!!
It was also multiple orders of magnitude more expensive.
As win7, the most common version will be these who is free with any new computer, usually the Home basic version who is limited to 8gb... WTF... 8gb... don't need 64 bit, a 33 bit will be enough !!!
There's no such thing as a 33bit CPU. I suppose someone could make one, but why? As I said, 64 bit is about the entire CPU architecture. There's a lot more to it then just how much memory it can address.
If everybody move to the professional, enterprise or ultimate version of win7, it will be perfect but it will not happen because these version is not what we can call cheap...
Why would someone want to pay double for a corporate version of Windows that only adds things they won't use? Home Premium goes up to 16GB of RAM, and the number of people who could actually get over that in a home PC setting is REALLY low (and for those people, there's Ultimate). Internally they're pretty much the same anyway. There's no reason Stardock would need people to be using corporate editions when making a 64 bit version of Elemental, unless they actually intend on using 192GB of RAM in the game (at which point they'll be reaching a userbase so tiny the game will never sell).
As myself, i am always using xp today... since 2005, i use xp pro x64... able to use a max 128gb ram ( i have 16gb ) and my two processor ( have two xeon quad core )... and i have not yet find a single valid reason for upgrade my OS !!!
Other then XP-64 having awful driver support, limited application support, and the fact that it's about to go End of Life and be totally unsupported for security patches (of which XP needs a ton given how insecure it is compared to 7)?