You ever noticed that it's mostly Jews that speak of "Judeo-Christian values"?
I think it's similar to the political situation in the county where I live. We have about 35% Republican registration, despite it being a VERY conservative area. So, when we run candidates we always talk about that they "share the same values important to Republicans and conservative Democrats." We know we're in the minority and need to tie ourselves to the conservative Democrats if we are ever going to win.
I think that's what the Jews in the United States do too. They know they're in the minority but are "drafting" off of the Christians.
If not, it would be quite a step for a believing Christian to convert to Judaism -- it would amount to "converting" from belief in Jesus to non-belief in Jesus.