Partially wrong.
One of the biggest complains a retail company gets is long lines. So they hire more people, however there is generally only so many registers. The amount of registers is determined in part by the foot traffic coming through the door (which is counted). Look at the difference between Lowe's Home Improvement and Wal-mart for example. Wal-mart has a LOT MORE foot traffic, therefore at least double the amount of registers that Lowe's has.
Now, concerning staff:
Many people work 9-5, and get off at 5, getting to many stores starting at or around that time as well. Therefore traffic is busier after 5pm. As such, stores compensate by having more registers open at 5pm-close, and on weekends of course. The registers have full lines, and many stores have a "no more than 3 people per line" policy before another register is opened.
Generally, there is enough staff to handle the store at all times, and more staff scheduled at night/weekends to handle the additional traffic. However, a store MUST balance those hours throughout the week, taking into account school schedules for college students, family needs for some families, etc. Therefore, the store must scatter the staff, keeping more people working night/weekends while allowing people time off in general, all while keeping each person at or under 40 hours a week. That's a lot to do, and a LOT that people don't understand when there are more than 3 people in line. "WHY DON"T YOU HIRE MORE PEOPLE?!"...
Yeah. For the 10 minutes that the store is flooded with people, on a wave of every hour? Not very good business sense there. As I said, the store generally has enough people, but must balance it as best they can. Sometimes, it is not enough for 10 mins here, 20 mins there in a flood of shoppers.
Lastly: Self Checkouts. These machines were designed for those complainers whom do not understand how businesses must work at balancing schedules and business needs, accounting for waves of traffic and lulls in traffic. These machines allow people to get through line a little faster on their own, to get back to their oh-so-much-more-important-than-you-tiny-cashier's lives. Also, it allows the cashier to open more registers at once, up to 5 at once.
It is NOT that there are less jobs for people. It is NOT a cost saving measure. The self checkouts would generally be closed anyway, save for EXTREME seasons such as Christmas, Father's Day, or other holidays that affect some businesses more than others. And, since people are not legally allowed to work more than 8 hours a day (Or, 40 hours a week without extra payment), those registers MAY BE CLOSED REGARDLESS.
The Self checkouts allows for those registers to be opened, freeing up employees to attend to other customer needs (Help desks, other service desks like Electronics or Lighting), and still allowing for smooth, under-3-customer checkouts.
Therefore, no, you should not get a discount cause you're not getting any less service, you're actually probably getting more, along with the business in general taking your busy-life needs more into account.