is perfectly acceptable: when you have a computer than isn't from 10 years ago, when there's not that big enough of a difference to buy W7, and when the main problem with Vista - the thing between the keyboard and chair - is actually sensible
There are several more reasons why to choose a 64-bit system of Windows 7; 64-bit editions of Windows need mandatory signing of all kernel-level drivers to make it more difficult for untrusted code to execute (viruses/malware/etc.).
It's partially true.
32-bit Windows uses PAE anyways, so it can use up to 64GB, the 4GB limit is just a licensing restriction (which can be unlocked, albeit illegally). 32-bit Windows Server 2008, for example, supports 64GB out of the box without any patches.