A link isnt everything it seems.
How do you show your past in the web design industry? With websites being upgraded on average every 3 years as designs and trends change, a clients site that you developed 3 years ago may no longer exist! And if they have not redesigned it since then, then they should have! and now it looks old and irrelevant so its not a good representation of your work.
So you really only have the last 2 to 3 years that you can reference.
But if in that time period you only worked on 2 or 3 sites but put in so much work to refine and rebuild and optimize and you cant see that in just one measly link to a site?
Actually, thinking about it, maybe web design is not so different from any other industry in creating a portfolio. Just because there could be a live link (which you may or may not want to link to currently) doesnt mean its any different. So its just a matter of presenting your work statically in a nice way on your portfolio without a link to the site necessarily because one link cannot reflect everything that went into a project. You have to do the work to show your work!