The owners of the 2600 web site replaced their links with text URLs, and so far are unpersecuted. Another way some might think about it is to consider that URLs can be used like access codes. But more to the point it is important to realize a link is not just like telling people the factual statement about what the access URL for a page is. You didn't just tell them where the page was, you actually built them a virtual button that, if they push it, causes it to be delivered. What's important about this is that from a legal standpoint, computers don't copy things.
People copy things, using computers as their tools.
The person who orders a computer to copy something in violation of a copyright is the copyright infringer, and the person who knowingly and deliberately built the system just to make that happen is a contributory infringer. You might do a site that inlines other people's materials and makes the viewer think they are actually your own. This can be a violation of the author's rights. It's worth pointing out that it is possible, though a pain, to build a web server so that access to internal pages is done through ever-changing URLs with magic cookies that only appear in the binding or navigating pages. This technique can prevent people from offering links to internal pages or doing inline inclusions of other people's graphics because each URL works only once.