Mealy mouthed letters are a tool for politicians. They allow them to sound like they support a cause (even if they don't come across as strong supporters) while retaining the freedom to change positions if their constituents start leaning heavily the opposite direction.
I rather wonder if those sending out such vague letters, while not being strong supporters of the RKBA, also will not be strong supporters of ban bills. If one hits the floor they may vote for it, but they will not be eager for one to come to the floor.
One of my own senators is like this- mouthed initial support for a ban, then quit talking about it and now she seems like she just wants the whole thing to go away (McCaskill, D-MO). The majority leader of the Senate (Reid) is on record saying that they won't even take up a ban if it doesn't look like passage is a certainty... I think Senators like this are why that is. They have no desire to stick their necks out and go on record if it isn't going to pass. So while they may not seem like our friends (and they really may not be), they at least have a sense of self preservation.
Was it Machiavelli who said "Let them hate so long as they fear?" I'd prefer that my politicians be true believers in the cause of the RKBA, but I'll settle for them understanding that votes to weaken my rights will mean loss of enough votes to get them looking for new work.