I really think it depends on the item!! Some items have huge markups and they still make money at 75% off, whereas with other items the markup isn't so big and therefore they may even take a bit of a loss.
I think the biggest problem is that due to forums like this and all the MANY bloggers out there, way more folks are aware of the cycles for mark downs, etc plus, management realizes what is going on and have chosen to cut back. I liked it better when it was mostly those of us who HAD to buy on clearance or do without that got the deals. Now folks who aren't single moms working for minimum wage and who have the time to "stalk" items make it harder for those of us who truly can ONLY buy on clearance after work or on the weekend.
And for those folks who buy out whole sections of stuff only to resell.....well, shame on them!!!