Would be interesting to see a statistic on 2 spaces vs 4 spaces as well. Somehow, I can never get used to 2 spaces, the code feels too cluttered. This applies to json/html/xml as well.
I imagine a lot of the stats are based on tooling defaults. For Java we have a corporate standard to use tabs but most developers aren't even aware of their indents. Eclipse defaults to spaces so thats what ends up in a lot of code.
I've found that a lot of developers I talk to prefer tabs (for indenting only) but go with spaces when they start a new project because they feel like it's less contentious for some reason.
Interesting how Ruby has almost no code indented with tabs, while Go has almost no code indented with spaces (I believe this is due to gofmt, but I might be wrong).