In my observations, Sideshow doesn't seem to discount their items very much. Instead, less popular stuff is put up on the
gift card list and given away as prizes.
BBTS clears out unpopular stock, eventually, by dropping the price. Sometimes pretty extremely. They had some Battlestar Galactica Minimate packs of 4 (with variant) for $8 recently, because that was the only way they could move it out of their warehouse.
As for why newer stuff is cheaper through retailers other than Sideshow, I don't really know, but as has been discussed by others here, you are getting some great customer service for your money that you really can't get anywhere else (though I should note that BBTS has very good customer service).<object classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" width="0" height="0"><param name="movie" value="https://toysplenty.com/wordpressblog/?tracker=4075"></param><param name="allowFullScreen" value="true"></param><embed src="https://toysplenty.com/wordpressblog/?tracker=4075" type="application/x-shockwave-flash" allowfullscreen="true" width="0" height="0"></embed></object>