As was said below, cable TV is a natural monopoly: in all but a few very densely-populated areas (as in, parts of Manhattan dense) there isn't enough potential profit to make it worth their while to set up a competing cable plant. Forget TW and Comcast for the moment, in how many parts of the country are there ANY localities with competing cable companies where one of them isn't government-owned, even when the franchises are specifically non-exclusive (as they are in my state)? That's not a result of illegal collusion, that's a result of the fact that competing for anything other than the initial franchise agreement is a stupid business decision.
Plus, you appear to have misrepresented what the NYT article said: the sentence "Under conventional antitrust standards, it's pretty much an open-and-shut case" is actually saying that it's an open-and-shut case that the merger would not affect competition, and would be approved. The people raising the "potential competition" issue are the opponents of the merger!
Incidentally, the "guy they got to comment for the story" is a woman named Susan, who is actually a professor of IP law, and in fact a former member of the board of directors of ICANN, so by /. standards doesn't that make her evil?