Because the web pages are being served over the internet, sometimes requested parts of the page don't make it. It could be for reasons of business firewalls, security programs, the browser being used, or a wide range of other issues that you can't plan for.
That's why some people here have been saying that they would put the links as a list, because that works better when there's no CSS, and the list is more flexibly manipulated by CSS to fit a wide range of situations.
Progressive Enhancement vs Graceful Degredation
It was only when the idea of progressive enhancement came along, that people realised that there is a much easier and more reliable way to get everything working in a wide variety of situations.
There's a good piece about progressive enhancement at What is Progressive Enhancement and Why Should You Care?