Frankly, what better way to secure a service than to disable it if you don't need it? Moreover, as long as it runs, it is vulnerable - and critical services will still run under full privileges under Vista, because they need those privileges. So yes, if you disable unrequired services, XP can reach a 'high' security level. Maybe not as high as Vista's, but considering the way security is implemented in the Vista kernel, these 'sandboxing' features are more than likely to be dispatched with no warnings and dire effects.
Unix' approach to services security is efficient in its simplicity: you make it own the files it requires or member of groups having read access to some other required files/devices, and you're set - even when compromised (which can already be quite tough), the service will be unable to infect anything that it doesn't own, and it can't modify (only read) the rest.
Yes, I've read the article. Following the advice in it, then the user would have full administrator access - making all security measures in Vista completely inefficient (merely wasting CPU cycles) - thus the fact that if you need to run Vista as administrator anyway, you're better off tightening XP's security: less insecure, less bloated (thus less possible exploits), cheaper and more extensively debugged.
I made my choice: I keep a lean, closed down XP on a spare partition (for a pair of games - goes well with the Fisher-Price look, that I've disabled anyway), and a nice Linux OS is now my main desktop (with security, 3D desktop, and responsiveness).