Publishers of websites take care of this part on their own. If they are providing some content on some page within their website and allowing views or downloads as per their policies without registration or with registration, they expect visitors to follow that.
If you register on a site, download the content and publish it on your blog; it doesn't seem a right act. But if you are providing a link to the page using which others visit on their page and they get the content only as per the provisions made by them then this seems to be a correct practice.
I am not a legal matter expert but I don't feel any copyright violation in providing the link on blog. In fact, if others do for my website pages, I will be happy. Moreover, providing links of other's websites and/or getting own website linked on other's websites are very useful in SEO (search Engine Optimization).
Please feel free to debate on these points in comments below.