I didn't miss that at all. If it said "Multiply by (charges per day / 5).", it would be wrong. Using that will give you the wrong price.
If you have an item with fireball, minimum level, 3 times per day, use-activated, unlimited charges, it would look like this going by Tome & Blood or the DMG:
3 (spell level) x 5 (caster level) x 2,000gp / (5/charges per day) = 18,072gp. That's price is only if you use 1.66 from (5/charges per day). If you round up by one decimal point, it would be 17,647gp.
If you use what you think it should say, it would look like this:
3 (spell level) x 5 (caster level) x 2,000gp x (charges per day/5) = 18,000gp. This is close, but incorrect by the book.
At 4 and 2 charges per day, both the rules and your viewpoint come to the same price. But they don't agree at 3 times per day. All I'm saying is that you don't really have any reason to complain about fractions when fractions were never even in contention. Also, the formula was further clarified in Tome & Blood. I will say, however, that your way is close enough that it works just fine, but that was also never in contention.
