You are reading too much into the word "Discount" It has a different meaning when talkin about bonds than buying something at a store. Well, sort of. In this case it is just a way for them to price in your profit when you buy it.
The bottom line is that you are taxed on your profits regardless of what you paid for it. Assuming you sell the bond for the full face value your clearly have a profit, regardless of whether it is a discount, coupon, a gift, etc.
This would actually be true of anything you buy at a store with a discount IF you later sold it back at a higher price.
Whether it is a discount or they just paid a flat fee for holding the bond it all comes out the same.
Investopedia Article on Bond Discounts