We're talking in the context of "truly great programmers". It makes sense that truly great programmers get that way by programming. That doesn't mean blogging is a useless activity, or that bloggers are bad programmers. Actually, I think most bloggers are good programmers, better than the average non-blogging population. But by and large, they aren't great programmers, because the jump from good to great takes that extra bit of concentration and attention that's consumed by blogging.

Think of programming ability as a pyramid. There're a vast amount of programmers that show up at work, put in their 8 hours, and never really think about what they're doing. These people generally don't read or write blogs. Then there're the people that are passionately involved in their craft. They blog. Then there're the people at the very top of the field - the Guy Steeles, Rob Pikes, Jeff Deans, etc. They usually don't blog, because they put all their concentration into their code, and when they take a break, they do things like photography or swing dancing that take them completely away from programming so they can recharge.

The interesting thing about this distribution is that the average blogger is a better programmer than the average non-blogger, but the average great programmer does not blog.

FWIW, I consider myself a good programmer, but not a great programmer. And I've suspected for a couple years that the reason I'm not a great programmer is because I talk too much and code too little. So I dunno if I'd tell the general blogger to shut up and get back to work, but I certainly tell myself to shut up and get back to work, usually with lukewarm results.