Also worth mentioning that Windows technically cheats. When you shut down modern Windows (starting with 8 AFAIK), it doesn’t truly shut down, it logs you out to the login screen and then hibernates. So when you boot back up, it can quickly restore state which makes it come up much faster as it doesn’t have to start everything back up from scratch.
45 seconds is a bit on the long end for Linux though, both my desktop and netbook boot in around 10-15 seconds.