Sometimes, the colors are too wacky, were experiments, or seasonal, too. So, it was just overstock.
I LOVE Homegoods/Tj's/Marshalls for these items. If it wasn't around, I would have MUCH cheaper items. But, I always go there first. Always a nice selection of OXO, Kitchenaid brand items.
And, celebrity wise - i got a Mario Batali bowl and Jamie Oliver casserole dish there for a song.
Someone else with more extensive/professional knowledge about this can probably give you more information, hopefully... but what I've found personally is that there is usually a cosmetic or otherwise minor issue with the cookware which deems it slightly irregular.
For example, I found a great LeCreuset cast iron dutch oven for about 1/3 the retail price at TJ Maxx, and I believe that it's because there were 2 spots on the top of the pot that were not fully covered by the blue paint (you could see the cast iron part) This doesn't affect the performance in any way, and it's barely visible, but does not meet the requirements to be sold as a retail product.
Usually, in my personal experiences at least, it's never been anything that makes the item work differently or worse than full-price, but that most companies have really strict requirements or a "checklist" that the product needs to pass in order to be sold at a retail store for full price.
Of course the best thing to do is to fully inspect the item (make sure the lids fit snugly, the bottoms sit on a level surface properly, any attachments are fully attached, no screws missing, etc), and celebrate your lucky find!
Same deal for me. I picked up a 6-3/4 qt oval LeCreuset pot that was marked irregular. The paint fade has small dots; it's not a clean fade, which doesn't meet with their standards.
I got it for $70. I can't recall what full retail is but I'm sure it's close to $300.
The Calphalon and All Clad products marked as irregular I've looked at were typcially scratched in come way. I've never seen warping.