Our founders, Daniel and Jason, weren’t actually big bloggers, but they were very active in online communities -- including some of the systems you noted above. They saw firsthand just how little innovation commenting had seen since essentially the beginning of the internet. There was a lot of low hanging fruit they addressed like fixing basic design and UX issues, bad spam filtering, clumsy admin and moderation tools, etc. But there was also a big vision they had around connecting users and communities via a common, networked platform vs. the isolated, disparate experience that commenting used to be.

That was in 2007. Today Disqus is a 40-person company (looking to hire more!: http://disqus.com/jobs) reaching 900 million readers each month across almost 2 million sites that have installed the service. Now, we have a whole other set of pain points and goals we want to address, so the work's never over :)