Brown is a Republican in a deep blue state. He HAS to at least appear bipartisan or he'll lose re-election. It would be the same if a Democrat is a Senator of a red state. Sen. Kerry, on the other hand, has views more in line with his state. Because of these underlying political dynamics, each Senator is doing what he needs to do. Why does Brown get praise for doing something he HAS to do for survival reasons?
Frankly, reporters' ideas of what amounts to political courage are almost always off. It is not courageous or praiseworthy to do what Brown has been doing. I think Kerry showed more courage going against his party over the years (just not maybe in a Right wing way) than Brown has.
Bottom line is this -- Brown is just not that impressive a figure. Apart from bipartisanship or partisanship (which like someone said upthread, is not always about votes but can be more subtle than that) he hasn't done anything remarkable in the Senate. His opponent, Elizabeth Warren, is far more compelling a figure IMHO. I hope Mass. makes the right choice in November.
Edit: Also, Lugar served a state far more right leaning than Mass. Snowe's Maine is also not as deep blue as Mass. Maybe the numbers just reflect the political realities of these elected officials' states? Maybe? Possibly?
I'm not a fan of political reporting like this. It seems like the reporter is revealing some great truth by citing voting statistics, but he doesn't talk about the politics about each state and there is also no distinction between big important votes and little votes, not to mention VITAL amendment votes which are oftentimes so much more important than final votes. So seemingly objective information is actually subjective or at the least incomplete information. I'm sure that Corker has a super conservative vote but he is far different from, say, Rubio, a truth I doubt voting records would reveal. (And that's another missing piece of information -- committee votes!)