I'd wager that people you see with "small sites, forums and blogs that can't scale easily to small numbers using relational DBs" are doing something wrong and they're probably going to have a long road in the NoSQL world as well. Just because you can make a query return the result set you want doesn't mean you've written the right query/schema design.

I assure you that there are plenty of performant sites running quite well on traditional SQL solutions that are FAR, FAR larger than those small blogs serving small traffic numbers that are having issues.