See designfestival is NOT a sub-domain or directory of sitepoint, so how on earth is anybody going to figure it out?
However, if you have xyz.com and then xyz.com/blog, with SAME theme, it's quite obvious that's they're SAME! (very few ppl know that if you install wordpress or any blogging software on a separate directory, it's treated separately by search engines!)
And, I didn't mean that everyone should do it!
There's definitely no clear answer to this question, but I suggested a work-around since updating your site weekly helps in keeping content fresh, and in turn getting better SERP, provided you do good KW research and link building!