Can anybody give me some examples of people who have done both? Personally I can't think of any. I know lots of guys with plenty of talent (sub-30:00 10k) and mileage (120 per week) who got stuck at 2:24-2:27. I know a few who got down to 2:20-2:22. I don't know a single one who has been able to break 2:19 without giving up full-time work.
Granted there used to be less incentive, because the OT standard was only 2:22. But still, do we know that 2:19 is possible for somebody who is working full-time?