A couple of other points, perhaps obvious but I think at least worth mentioning -
1) Many tickets are refundable and most are at least exchangeable. Therefore, there is a good chance they won't be flown exactly as purchased. It would not make sense to award miles to these tickets before they are flown, and it would be extraordinarily complicated to award miles at the time of purchase to one kind of ticket but not to others.
2) You could always go to the airport and check-in for your outbound flights and at least get those miles.
3) If you just want to buy your miles, that can be done in other ways for (typically) 2 cents/mile. For your roundtrip ATL/LAX/ATL (which is actually about 4000 miles), you could just purchase those miles for about $80, less than half of the $198 fare you quoted.
[This message has been edited by JerryFF (edited 07-09-2000).]