Presorted Standard is cheaper than First Class. First class is sent with some expectations on whether it will be delivered and how quickly. Standard is "best effort". If a company wants you to pay a bill, then they want to make sure you get it, they pay extra for that stamp. If a company wants to send an advert that they know you are going to throw in the trash anyway, they cheap out.

But for the life of me, I have not been able to figure out the price of a Standard stamp. USPS sells stamps online, but you'd think it would be easier to find the price, but still I can't find it. I would love to know how much is spent on mail that no one really cares about.