Hard 17 with dealer showing 10

[Double Down]

In Professional Blackjack by Wong, 17 vs. A you should hit if count is -6 in a 6deck game where dealer stands on soft 17. If surrender is available, surrender vs ace if the dealer hits soft 17. But there is no number in the matrix for 17 vs 10, so you shouldn't ever hit or surrender.
But you have an interesting point. I've often thought about this a lot, when the count is HUGE and you have 17 vs his 10. I'm sure if you run the numbers it will show that it's still not correct. Coming from a common sense point of view, it's probably because even though the dealer's chances of having a 10 underneath is higher, so are the chances of him busting on the times when he has a small card underneath.