It's sorta BS.
Vista is probably going to be much touchier about what sort of changes are allowed before it requires re-activation. But a phone call to get permission to install a video card isn't that big of deal.
The EULA allows you to install it on two different computers (one at a time) before your license is used up. With 'two different computer' equalling 'two different motherboards' if there is a dispute on what constitutes a 'new computer', baring any replacement of defective parts.
So that is the change with Vista _retail_ versions. They mellowed it out some compared to what it originally was suppose to be, but the details are iffy.
The other important change is that they added new restrictions on weither or not you can run different versions in a virtual machine.
Most people are going to be using OEM versions, so that is what matters. It's the same as XP, one machine one copy whatever hardware upgrades you want. (most people get around that anyways. The MS people working the phones only seem to care rarely)
So it's not realy any different then what your used to.