Funny how no one is questioning whether or not the campaigning activities of George W. Bush are interfering with his duties as the sitting President. Maybe he should resign the Presidency while he campaigns for re-election.
He can perform (and is) the presidential duties from anywhere in the country. A Senator, however, can only vote at the Capitol.
I was being facetious with the Bush comment. Anyway, if I was a resident of MA or NC, I wouldn't be too concerned if one of my Senators didn't participate in a debate and a vote on whether or not to continue debating an issue.
The missed vote was not on the amendment itself, but on cloture -- whether or not to continue debating the issue.