Potresti anche provare EXISTS:
select count(1)
from customers c
where exists (
select 1
from accounts a
where sid in(72,73,74,75,76,77,78,79)
and a.custid = c.custid
)
and not exists (
select 1
from accounts a
where sid in(80,81)
and a.custid = c.custid
);
Potrebbe essere utile leggere:Differenza tra EXISTS e IN in SQL?