12 and 13 in high counts and wild cards
With most counting systems we do not account for some very important cards in this situation. A 7 can turn a 13 into a winner and an 8 gives you a hand that can not lose. An 8 will turn a 12 often into a winner and a 9 gives you a hand that can not lose. These are wild or unpredictible cards for you with these hands or for the dealer if the dealer is the person with the 12 or 13.
These are the kind of hands where if computers were legal, you might see the advantage of computer counting compared to our counting systems because unless you are Rainman, you are not keeping side counts of 7,8 or 9.
It really comes down to not if you will win or lose with your 13 vs 10 but how much you are going to lose over time if you hit on it or stand on it. Though your hand is a net loser, every simulation ever made shows you will lose less by hitting than standing on these low stiffs at just about any count.