Estate Tax Mystery Solved?

The federal estate tax officially expires on New Year's Eve, even though the House of Representatives voted for a temporary extension. Why wasn't the Senate willing to go along?

At The Christian Science Monitor, David R. Francis offers a possible clue:

[W]ith 46 to 68 millionaires in the Senate (the count hangs on whether one uses minimum or maximum net-worth numbers), will the chamber vote to maintain a tax that could damage its members’ own estates? Because 22 senators own at least $3.5 million and 14 own at least $7 million, should they recuse themselves from a vote that so directly affects their interests? The Center for Responsive Politics calculates the average wealth of US senators in 2008 at $13.9 million.