On the first aspect, the pay scale was set by the Afghan government, and it's in keeping with the responsibilities and things they are doing. I realize that from $70 to $750 does seem like a lot, but given the level of complexity and the responsibility in what they're doing, those would have been factors they considered when they designed the pay scale.
Second patrolman, at the very bottom, is your recruit who is starting out, and $70 dollars may not seem like much to us in our country, but to someone there....
Do you remember what I said Afghans were paid per day when they were being hired to work in the opium fields? While on the surface $70 doesn't sound like a lot, it is a reasonable basic salary.