I agree that, all things being equal, you would want to support as many features as you can. But you do not want to support a feature that would make your product run slower on a majority of your client machines.

If you add two 64-bit numbers on a 32-bit machine, the process takes twice as long. Even if you are just adding 1+1.


Even after the release of Vista, most machines on the market will still be 32-bit. So 32-bit applications are still going to be the norm for most Vista applications (at least for a while).