Sure, there will be thoughtless people who make that comment - many of them. But, how many of them ever got to the point of being their party's nominee? What I saw were two party elders, respectfully sitting together. Not to mention - between them they got more mention (from what I saw) than any other pair. (Look who the NYT interactive tool chose to spotlight -
http://www.nytimes.com/2011/01/26/us/politics/26scene.html?partner=rss&emc=rss )
The comments are so junior high (or middle school) - and as all our parents told us - especially those of us who were thin skinned - we need to consider the source. The fact is that JK's position in the party was enhanced by his run and his actions since then. McCain is a different situation. He was a super media favorite and he ran a miserable campaign. But, from the moment he lost, the media was still there for him arguing that he could be the leader of bipartisanship with Obama. This was two party elders, with a long mixed history between them, sitting together. JK designated as such because of his steady important work gives him grudging credit and McCain because the media sees a spark of potential greatness. Not to mention - they were the nominees of opposite parties during the last contentious decade. There is some symbolism there.
As to pick another Republican - who would you suggest? I had though Dick Lugar, but I think that could have potentially hurt Lugar - who is up for re-election. In addition, Kerry and Lugar sitting together speaking bipartisanship reflects what their relationship always was - nothing new. Scott Brown? Why wish that on Kerry? - and you know that would generate negative tweets - and comments praising Brown at Kerry's expense. (Not to mention - you might notice that Brown has been almost not mentioned and at least on MSNBC rarely seen as they scanned the audience - and he was squirming each time. Kerry was - especially for a longish time when Obama spoke of Sudan. Why get Brown more TV time?) Inhofe? Rand? No way. The only one I could think of that would come close to McCain in symbolism is Kyl - and that would be lost on the TV viewers. Why Kyl? If you watched the healthcare debates or the New START debates, Kyl is one of the sharpest of the Republicans in the Senate - as Kerry is on our side. But, I think of Kyl more as a Republican Schumer - because although both are as sharp as Kerry, neither can inspire their side with their eloquence or vision.