OK, I see now. The idea that it is a "throw away" roll was completely lost on me. Hell, even the beautiful character sheet from this site has it listed with the other Ability scores. If I had understood this, then I would've been able to answer my own questions.

It's funny, I completely understood the mechanic behind usurpation, but I wasn't 100% sure I was playing it right because of my confusion about the score.

I agree with Cuchulainshound, the fact that the ability rolled for bloodline score is a phantom ability needs more Clarification.