Dead cards and counting outs.

[OrianasDaad]

I'm likely missing something very simple, but in my quest to understand, I must pose the question.

How come, when you are counting outs, you don't subtract the probability that one or more of your outs are dead in other hands? Numerous books and articles all use the term "unseen cards". Part of me knows that this is correct (because it isn't challenged), but another part of me wonders why this is correct. Lets use an example.

You've got an open-ended straight draw on a rainbow board with unsuited cards. Precisely 8 outs, with 47 unseen cards, or 1-4.875 to make your hand. Let's also say that 9 other players got cards. Without doing math I'm incapable of doing (yet), I'm going to assume that on average, one of the outs is going to be dead. Wouldn't you need 1-5.71 to draw to your straight, instead of 1-4.875?

I feel that my logic is wrong somewhere.