So how can OpenDNS do a better job than your ISP? It's no surprise, really—ISPs like Comcast differentiate themselves from each other by:

• Price.
• Download Rate, which is the easiest component of perceived Internet speed to understand and can be easily measured even by average users at various “how fast is your connection” websites.
• Inflaming fears of poorly-understood security threats, then promising to protect users from teh haXors with a raft of software, most of which is free anyway or is no better than free alternatives.
• The strength of their respective web portals, which is so pathetic a strategy it deserves no further comment.

I've never seen an ISP advertise superior DNS servers—DNS reliability just doesn't sell anybody on the service. But OpenDNS, on the other hand, does nothing but DNS, so they are motivated to do it right.

By the way—some might look at the above list of non-resolved domains and notice that the contents of these sites are all of a conservative or libertarian bent, and begin to imagine that Comcast has some kind of spooky Agenda here. So let me quash that right now: please don't get political. I seriously doubt that Comcast is seeking to block your access to sites of any particular persuasion, and I suspect we could turn up plenty of examples on every side of politics that fail in the same way—the list above is just a couple of sites I'm aware of right now that don't work. Before slinging that word “conspiracy” around, take a deep breath and try to remember: Incompetence is almost always a better explanation than Malice.