NooB Question: Why are WaterSense toilets so much cheaper than standard toilets?

Hey guys,
I am doing research because I want to buy new toilets for my house. I was thinking about American Standard, so I went on their website. After looking at their products, I noticed that the WaterSense toilets were MUCH cheaper than their standard, non EPA-certified toilets. Can someone enlighten me with the reason why?

Thanks in advance!

(1st post! Woot!)

It might be volume...many places are requiring water sense toilets. Read Terry's toilet reviews. Lots of comments re: AS stuff.

Normally the Watersense (1.28 or less) and the 1.6 are similar in price.