How many non-nerds do you know that even know what DNS is? Yes, slowly people will learn 'just type in the numbers xyz into your address bar', but it'll be a rather big obstacle for most casual users.

On top of that, if it turns out that a DNS block is insufficient to stop the majority of Belgian users to access The Pirate Bay, it's a small step to go back to the judge and ask for a more stringent block.

This is a first step, but a major one - it will set a precedent not only for Belgium and similar sites with pirated content, but also for other European countries. It'll be interesting to see how this pans out, and if there will be a counter-movement of sufficient weight to instigate legislation that will overturn broad, sweeping blocks of content. I suspect not.