You can update the software without pulling it down. In order to use the update you need to restart, but there's a large difference between restarting a service and restarting an OS. It isn't really analogous.
Neither of those support your original claim. The author is focused on one specific feature, which is nice but excludes the entire shutdown process and booting up until the Windows logo appears. Anyone who's run a server knows that just the BIOS initialization is often much longer than 10 seconds. And, of course, many services take a noticeable amount of time to startup so time-to-available is longer than time-to-login-screen.
Worse, the conversation was actually about the time needed to install updates. Now that Windows logs out before installing updates, you have a fairly sizable time delay – tens of minutes after a large update even on an SSD – while the service is unavailable but before the system starts rebooting.
How does Fast Boot work? Well, it's actually not booting at all – it's logging out all active users and hibernating:
That's a really nice bit of work in normal usage but it means that you have to do the standard cold boot process when you're getting a system update. That means that a sysadmin would need to review each update to know whether it would trigger a fast or slow boot, assuming that a patch for e.g. SQL Server wouldn't always trigger a cold boot to be conservative.
The alternative is what everyone's been saying, namely that you have to assume that a reboot is slow and have n > 1 servers if uptime matters.
