Much better use of multicore CPUs
There is a little more power mgmt stuff, but I wouldn't call it "much better".
GPU acceleration of the GUI
Windows NT has always supported GPU acceleration of the GUI through the display driver. The DWM just uses it differently, mostly for 3d effects and caching window contents.
What does this mean? DLLs have always been mapped COW in processes, and SXS was introduced in XP.
You can use the fancy aero and desktop composition effects in RDP6, in Vista, plus support for more device redirection. This is nice, but mainly eye candy. Not a vast improvement. There isn't much substantive that you can do with RDP 6.1 that you couldn't in 5.1. Or NT4 TSE for that matter.
vastly improved central managment and deployment features for businesses
Group policy, with MSI installation, net boot installation, etc. existed in their current form since Windows 2000. There have been improvements, but no vast revolutions.
Easy 64 bit usage with drivers
XP had AMD64 support first (albeit with the WS2003 code base). The drivers are finally catching up. This is mainly the job of IHVs, not Microsoft. The drivers that Microsoft traditionally provides (most of them, really) were ready in XP64.
Yes, Vista now uses an image based install that supposed to be much faster.
Better power managment and usage of hardware suspend
2000 fully supported ACPI power modes. There have been minor refinements since then, but noting major.
better usage of memory (cacheing for very noticible speed gains)
SuperFetch (new in Vista) does pre-emptively fill unused memory with things that were paged out or the OS otherwise thinks you may use. To support this, the kernel now has 8 memory priorities, which help a lot in determining what should go first when memory gets tight.
XP had MCE first.
transparent Bitlocker hard drive encryption (in pro and ultimate) with TPM
Note that per-file encryption has been supported since 2000.
program execution isolation that redirects reg and file system calls to safe locations
There have been some redirection shims since XP at least.
epiclly better wireless support
Epically? It certainly takes more clicks to get into the adapter list control panel. There are automatic locations in Vista that automatically config your firewall and such, but XP works fine if you just want to connect to the network.
support for propper GUI scaleing on high DPI LCDs
It's better, but there's still a lot of apps that break
Automatic driver retrival for most hardware right of Windows update without searching
XP will offer to search for drivers for unknown hardware, and include driver updates in Windows Update.
Faster boot times and UI responce on semi-decent hardware (compared to XP)
XP has prefetching and a lot less to load than Vista or "7". Why would the UI responsiveness be any better?
Windows 7 does have improvements, don't get me wrong I'll probably upgrade to it, but it's not making a major advance in every area. XP still does most of what 7 and Vista do, and using less resources. Besides, Vista was the major version change to 6.0.