To be honest, "they" are more likely to be using T..Wi..Tt..eR Firehose and equivalents for Facebook etc.
Don't know much about Disqus, I suspect its probably one of those trend following things,and perhaps it has decent website integration. When someone brings out a better alternative, the meeja will probably shift to that. Also, I suspect some major outlets such as the BBC, CNN etc don't use Disqus.