Absolutely, positively.

The idea of yield management is to fill the plane and obtain maximum revenue. It's based on historical demand statistics for the route, date, time of day and everything else. If history suggests they'll fill a plane at full Y, that's all they'll offer. If it suggests they won't, they'll offer lower fares - but only low enough, and only enough of them, to fill it - based on historical patterns and fancy statistical analysis.

The airlines invented yield management, are pros at it, and usually come close to the mark. Sometimes they miss. When they miss high, they bump people. When they miss low, they offer more discounts at the last minute. The Web has given them new ways to do this, so they have more incentive to miss low - that is, to restrict discounts early.