You are correct that no sites have been updated since February. When you ask why is it so important, it's relative to who?
To your visitors because it gives them some assurance that the site is somewhat reliable
To you because you want to set a good impression for your visitors. You also want to have a site that is considered worth buying or linking to or from whatever your objective is.
It is important to Google because they want to maintain their image of giving value to their customers.
I personally believe that pagerank is overated. If a site has authority because those who matter link to it, it will rank well anyway so branding becomes more important. I think most in the IM world, including Google realize that PR can be faked and engineered. That's why Google keep bringing out all the farm animals to prevent that sort of thing.