SEO specialties tell you that your blog should be at your site so that our site will be more active and you will be ranked higher.
Blog is like a advertisement / billboard / banner ... Do you put those inside of your company? No, you put them where people are ... So Bloguru is just that site. Thousands of people come to Bloguru that make it very popular.
SEO / Marketing specialists tell you that it only makes Bloguru popular not your site. That is a bad thing. That a such a bull. If your Bloguru content contains the link to your side ...which you should, it is like people are talking about your ad. That is good thing. If you advertise m=on TV, do you want to run only on your website or national TV station?
What is the point of running Blog on your site? Run it where people are.