Windows Updates w/o Restart

I don't know a whole lot about Windows architecture, so I'm wondering : Would it be technically possible to install the updates without the need to restart the PC?

For example, back when IE9 was in Beta (Feb. 2011 IIRC), you had to restart in order to complete the installation. Instead of doing that, there was an option to kill explorer.exe for the duration of the install and then restart that process. Nothing else.

Could something like that be implemented for the more complex updates?