Chait and Yglesias are annoyed by Senators who, as Matt says, "have a very annoying habit of trying to avoid accepting responsibility for their own decisions. Instead of 'I don’t want a public option' you get a lot of talk about vote counts and bipartisanship."
I can't tell people what they should find annoying, but of course politicians facing a tough vote are going to try to shift blame and duck opportunities to state their positions clearly. Chait says he "find[s] it odd that reporters interviewing Senators allow them to avoid taking positions by acting like pundits rather than participants." Reporters, however, don't have the ability to allow or not allow Senators to answer questions as they see fit. Granted, a reporter can emphasize that a pol is ducking a question, but there are simply a lot of situations in which being called out for avoiding a straight answer is worse for a pol than actually giving a straight answer. And most Senators have pretty good skills at this sort of thing.
Part of this is one of my favorite themes: it's not reasonable to expect poker players to tell the truth while the hand is still being played. Part of it is a freakishly large, but quite reasonable, fear of being perceived as a flip-flopper. Bills are complex, and Susan Collins or Olympia Snowe or Kent Conrad can probably imagine a health care bill they would vote for and a bill they would vote against -- and specific provisions (e.g. a public option trigger) they could vote for or vote against -- depending on how others vote, depending on the political situation, depending on the details of the bill or the provision, and depending on how other bargaining goes. They don't know yet, and they aren't going to tell us. Even if the language they choose to do so annoys some people.