A better index is http://LangPop.com, which I recently sold on to a new owner, who hopefully will be working hard to spruce it up some, and add some new languages like Go, although Go is always going to be problematic in search engines.
Not sure if stackoverflow tags are a great indicator. TIOBE tries to use job listings and google trends. Searching job listings/search engines for 'go' probably wouldn't return much results (because of the ambiguous name) which is why its a lot lower than it should be.
The two are not mutually exclusive. Rather, I'd think they're directly proportional. A very straightforward and simple yet popular language should have very few questions, which doesn't seem to be the case; conversely, brainfuck is particularly cryptic and should have many questions, yet it does not.
StackOverflow is admittedly .NET heavy, but since SV is somewhat anti-Microsoft, perhaps this will balance things out.
2. It lets you fiddle with the 'normalized comparison' to weight the sources differently. If you play right, you can make your favorite language win!