I think they expect businesses to use more traffic, and to require more expense to support.
Practically all Internet service is oversubscribed to some extent. The uplink is maybe 1 gigabit, but the downlink that has been sold is maybe 30 gigabits to 200 gigabits, when you add up all the customers. It is actually a feature of the Internet, that you don’t use any bandwidth when you don’t send anything, and you have the full bandwidth available to you when nobody else is sending anything. You can’t afford high-speed Internet if you had to pay for all the bandwidth yourself.
The problem comes if you use the bandwidth a lot. For most of the day, home service is idle, with a peak in the evening when everybody is watching YouTube and Netflix at the same time. And that traffic is mostly downstream, so a big company like Comcast can receive it for free, or even charge the source for “transit.” Businesses peak at business hours for their time zone, and a lot of businesses have a significant amount of upload traffic. If your company successfully expands overseas, then it will be uploading all the time. In theory, business plans cannot be oversubscribed as much.
If your web site doesn’t use HTTPS, then the big ISPs also tend to do deep packet inspection, and some of them inject their own ads. Fun times.
Of course, there are also captive audiences and rent-seeking.
if by discrimination you mean guarantees versus best-efforts. business class services, speaking generally, are less or not at all over subscribed while providing contractual guarantees to service performance and problem resolution.
residential is best effort. they'll do their best to keep it up and give you the speeds you pay for, but if it doesn't work out that way sometimes, well, they're sorry about that.
Price discrimination is an economic concept - charging different prices for very similar products or services to get the value that each customer is willing to pay. That is often difficult and what normally happens is each customer is charged the same price.
