My experience kinda align with that believe. This is not really a technical/business strategy thing with the airlines, but work pattern (imo). Office workers get off work on saturday/sundays, so I believe that more "work" is put into place during the weekdays. Airlines look at previous week sales and inventory on monday, release the prices/availability on tuesday/wednesday... On the other side, most people get saturday/sunday off work, so they are shopping for their tickets (paid or award tickets) on the weekends, so availability from friday to monday is poor.

My personal experience searching for award tickets (Delta/UA/AA/BA) is generally poor friday/Saturday/Sunday. However, this is from my mind... I am not keeping good notes, nor using scientific methods...