Ours has clearance racks almost year-round, too. It's the first place that I stop when I go to Lowe's...or if I'm near Lowe's, or passing by Lowe's, etc.
I wonder if the big garden-center-wide sales may be a northern thing. I know some garden centers completely shut down for the winter. They continue to sell plants here all year. They do tend to mark down a lot of things right before the Christmas tree shipment comes in.
Still, I may try to go by there soon and see if there are any good sales going on.
David is right about the way plants are sold at the big box stores. At HD, the wholesaler comes in and takes away any unsold plants. I guess they just throw them away.