Why does not having my router switched on stop my computer from booting?

Just out of curiosity, I tried to boot my desktop machine last night without switching on the router. I didn't need internet access for what I wanted to do just then. To my surprise, it never completed the POST. When I switched the router on, the bleep announcing the end of the POST sounded immediately and the elilo menu came up. Today I checked, and the behaviour is consistent. Is this normal for modern computers?