I can think of a number of scenarios that aren't that simple
@ozfflyer, for example:
Commercial TA hands back seats from a block booking they have been unable to sell (generally in discount fare buckets). Depending on the time decay until flight and likelihood of sale (based on day of week, destination and previous data on time of year and loads), YM will decide on a strategy of which fare buckets to put the seats. Then Marketing will put together campaign to sell seats (social media channels blitz, flash advert on website, or add to existing campaigns as some examples).
So
@neean prices can drop (where flights have low seat sales and the time before departure is nearing); whereas in normal conditions, the first seats sold are generally in the lower fare buckets (but with greater conditions), so prices are seen to go up because the remaining seats are the more expensive ones (but with flexible conditions). Most pax are happy to take the restrictive condition flights if they don't need flexibility (or don't value their time as much as others, particularly business people).