Although you may argue that they are limited to one link per post, they are actually able to post more than one link by enclosing it with ``s (and other ways), so making it so that they are not allowed to have any links in their post would simply mean that one would not be able to click on one of them and be redirected to wherever the link is linking to. And as I have seen many spam posts with links to malicious websites, I think that it would be good if new users (until they get to a certain rep) be not allowed to have any links actually acting as links in their posts at all.
-6 and no answers, I'm no expert or mod, but here are my musings on why links are allowed by new users. It is simply the lesser evil in the situation, we need some way for them to give us screen shots (you can imagine what horrors could pop up if anyone could post a screen shot), also what about things like bug reports or sys logs? We need to see these to help people but if they can't post links, then how?
New users need some way to provide us with the information needed, they are our bread and butter, and we need that info somehow, links would seem the least messy way to do this.
If you were to ban them from links till say 50 rep, what alternative would you provide them to get their log etc. to us ?