An answer
"why do you stand on a 16 against a 10 in a positive count?"
Of course the correct answer is because statistical analysis shows we lose less by standing than by hitting. At a near neutral count, we lose roughly 2/3 of the time no matter if we hit or stand.
But I suspect you want an answer in layman's terms to explain why that is so. Sometimes it helps to think of extremes in such cases. Picture a situation in which all the unseen cards must be tens except for one small card. If we hit, we are likely to bust. And if we don't bust, the small card may be too small (an A,2, or 3) and the dealer's 20 beats us anyway. In other words, no matter if we draw a big card or a small card, we seldom win. We have a better chance (very small chance, but still better) to stand and hope the small card is the dealer's hole card.
Now picture all the remaining unseen cards as small ones except for 1 big card. If we stand, the dealer may have that 10 in the hole or is likely to draw one or more small ones to make a hand & beat us most times. If we hit, we would seldom bust with only 1 big card remaining, so it is better to hit in low counts.
"Isn't the dealer just as likely to have a ten in the hole as you are to get one on the hit?"
Yes, but if the dealer has a ten in the hole, you are not likely to win anyway as outlined above. It is better odds in high counts to take a chance that the dealer has a stiff (assumming surrender is not available). No matter what you do, this is a very negative EV hand. The strategy here is structured to minimize the loss, as there is no way to escape it.
"Also, why do the blackjack authors say 'A positive count is good because the dealer has to hit his bust hands-you don't" while the counting indices generally only say to stand on 16 in a positive count- the count has to be like +80 to stand on a 13."
The authors are referring to generally standing on your stiff when the dealer also has a stiff. Although it doesn't seem like it, dealers do sometimes have something up besides a ten. I think they call those aces.