Microsoft have been using deception to make Windows (and now Windows 8) seem faster for years. Windows XP went very quickly to the desktop, but it could take a whole minute (or on very slow machines, several) for it to fully start up.
Windows 8 is full of animations, to disguise latency.
It's a well-known technique used by a lot of products. Github, for example, has a little "slide-in" animation of when you click on a folder in a repo to achieve the same latency masking.
I don't think this should be seen as a negative or bad thing. But it should put things in perspective for those comparing the "performance" between different platforms and OS's.
Another similar example is how Apple doesn't show a pop-up message when an app crashes in iOS, while Android does (Force Close), which makes people think Android crashes a lot more when they keep seeing these Force Closes, even though there have been some reports saying that iOS apps crash more often than Android apps on average. But the perception matters a lot more.
Although in some ways the quick to desktop thing in XP actually achieves the reverse - it creates the impression that you spend a long time waiting for the Windows GUI rather than the one-off boot process, which might have been a better scapegoat for them.
They made that decision back when people expected to reboot at least daily, and "shutdown at night" was still current advice. It could have gone either way, I guess.
Irrelevant. The truth is, both OSs are designed to give you a basically usable, interactive system before all startup tasks are finished. There's no reason not to this since it doesn't matter if you get a shell prompt before e.g. sendmail is started - even if you manage to write an email in the interim period, it will simply be queued until sendmail is started. But it's not a "deception" when Windows does it; everyone does it.
Imagine a car that didn't let you drive until the aircon had reached the desired temperature...
Windows 8 is full of animations, to disguise latency.