The problem is that this appeals to their constituencies and they will get re-elected. So, blame belongs to the voters too.
You are right, Snowe and Collins politics are absolutely expected detestable as they are. Add Brown in Mass. and now the most liberal member of the senate by far, Mark Kirk, so called "republican" Illinois.
Kirk has a 10 year record in the house, that makes him more liberal than any member of either House calling themselves Republican and furthermore he puts most democrats to shame in the liberalism department.
All I'm waiting for now is for him to "come out of the closet" ala Barney Frank.