Even within the realm of writing-about-statistics, there are things I can say in a blog that are much more difficult to include in an academic article. Blogging gives me freedom.
But I want to distinguish between two different sorts of frankness.
1. Obnoxiousness: In a blog I can write, “I hate X” as rudely as I’d like without needing to justify myself.
2. Openness: In a blog I can write about the limitations of my work. It’s a real challenge to discuss limitations in a scholarly article, as we’re always looking over our shoulder at what referees might think. Sure, sometimes I can get away with writing “Survey weighting is a mess,” but my impression is that most scholarly articles are relentlessly upbeat. Sort of like how a magazine article typically will have a theme and just plug it over and over. In a blog we can more easily admit uncertainty.
Overall, I think blogs are more celebrated for feature 1 above (the freedom to say what you really feel, to be rude, partisan, and politically incorrect), but I think feature 2 (the freedom to express uncertainty) is important too.