The latter means it's far easier for 64-bit drivers to be compiled, and to that end the 64-bit versions of most any distribution have the same full complement of drivers as their 32-bit counterparts. The end result: Windows may have support for just about every hardware device out there, but only if 64-bit support's not part of the equation.
In Windows, the 64-bit barrier shows up in some other minor, but annoying ways. Both 32- and 64-bit IE is included with the x64 editions of Windows, but if you plan on using the 64-bit version of Flash, keep waiting. Flash only works in the 32-bit incarnations of IE, Firefox and so on.
Official support for 64-bit browsers is planned later this year. On the Linux side, unofficial, but solid support for 64-bit Flash playback is out there right now -- although the level of implementation may vary widely depending on the distribution. Ubuntu, for instance, seems to have the most reliable handling of such things; with other distros it's more of a piecemeal crapshoot.
If you're committed to moving to 64-bit Windows but have no drivers for some crucial hardware, there are a few workarounds. One is a variation on a plan that Microsoft is hatching for Windows 7's official release: use a virtual machine, running 32-bit Windows, to enable hardware for which only 32-bit drivers exist. This can be done in Windows right now -- in fact, I did it using VirtualBox and a spare copy of 32-bit XP to get my scanner and printer working, neither of which were supported in any 64-bit edition of Windows.
It may also be possible to pull off the same trick by running Linux in the virtual machine. VirtualBox is particularly useful for this since it allows you to directly connect USB hardware to the virtual machine, even if said hardware has no driver on the host side. But if you have no overriding reason to move to a 64-bit edition of either Windows or Linux, odds are you can stay 32-bit with the next iterations of both without losing out on anything.
As someone else once put it: "It's the software, stupid." No operating system is going to be worth the trouble if it doesn't support programs you use. Windows 7 has a distinct advantage in that it supports all of the software that ran in Vista and XP, with only the most minimal of exceptions.
If you endured hassle getting programs to work in Windows Vista, most of that was probably due to the way Vista insisted on only running programs in non-administrative user mode. In the three years since, just about every program released for Windows or updated since is now "Vista-aware", and behaves appropriately. Windows 7 doesn't change this situation, so any existing Windows programs that worked under Vista should work in 7, too.
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