Well, let's get some correct info here. You can get to the blog from BPL, just not from every page. I assume that whoever built BPL didn't use master pages, since the links in the menu banner are inconsistent from page to page. But if you click on "Blog" from the BPL home page and some others, it indeed takes you to the blog.
From the blog, the menu banner at the top takes you to various places on BPL and nowhere else - to the BPL home page, or the articles page, or the subscribe page, etc. So while it seems to be hosted elsewhere, it's really part of the BPL family, so to speak.