Apple takes a hefty 30% of all subscriptions through the Apple Appstore, my guess is that the 10 dollars you are paying extra is to cover that fee. So: sign up through the website and you'll have the same advantages, without paying Apple for that
I seem to have a similar problem... Although my stats say I have found 146 caches (146 distinct), my PQ only gives me 144 caches..
Any ideas on that one?