When firms offer price discrimination (that's what this is called formally, offering different prices to various classes of consumer) they are making more money by taking the consumer surplus that would have been made (the extra money a consumer would have paid for the good).

Think of it this way: a rich man is willing to pay up to $10.00 for the chicken breast that his family needs for dinner, but his blue-collar cousin can only afford $6.00 at the most. Had the grocery store only created one line with the price of $8.00, their revenue from these two consumers would be only the rich man's sale, 8 dollars. If, on the other hand, the store had two lines, one for $5 and one for $10, they can make 15 dollars from these two shoppers!

Hope that clears it up.