Quite a bit of (in some cases contradictory) info has already been given out. Here is my experience (though it is old since I've been out of retail and sales for a decade now).
Discount rates vary from store to store. Most of my experience was mainly with department stores where it is typically about 20% (we got the discount on sales and clearance items, and when there was a good sale, plus a coupon sale, and our discount, it could be a nice discount sometimes).
The OP seems to assume that all retail sales associates make very little. Now it is true that many retail jobs suck, some pay pretty decently. It is all over the board, but I would assume that at higher end retailers (where it is usually a commission based pay structure and high dollar items) that pay is pretty good.
Today, most retail is a straight (and low) hourly rate, but that isn't always the case. In the early 90's when I worked at Macy's many still paid almost everyone on commission. At a good location, you can make good money selling retail on commission. I found Macy's to be a pretty comfortable existence for a 22 year old young man (I shouldn't have left when I did, but I wanted to try something else and left retail). When I worked at Hechts (local DC/Baltimore area store that was bought out by Macys a few years back) the sales associates were hourly but some departments were commission. I know many of the salespeople in the men's suits department made quite a bit, often more than their managers. A few years after I left my sales job there I went back to another Hechts store as a manager. One of the store managers at the store where I worked a few years earlier when I was a sales associate worked at my new store as a salesperson in the men's suit department and she certainly did not see it as a demotion. She made more money and had better hours than she did when she was a manager.
Of course, there are some quirks to a commission retail position. With a draw instead of a base wage (i.e. if you don't sell enough to cover it one day, say during a day shift, you have to make it up when you work a better shift), and with the full-timers staffing the store at low traffic times (the store needs staffed in the morning and afternoon on weekdays even though there may not be a lot of traffic) and part-timers coming in at high traffic shifts (when they are most needed), part-timers would often make as much, and sometimes more, than full-timers (a full-time associate would often have fewer good shifts than the part-timers). Also, a bad location and low traffic can be murder on commission and result in very low pay, while working for the same company in a higher traffic area can be quite lucrative. Then if you are unlucky and work more than one location you may have trouble developing repeat customers.
So, anyway, I guess the bottom line is that there are a lot of variables that can effect what a retail salesperson will earn. However, in a good location, a commissioned salesperson at a high end retailer can make a very comfortable living (one that can often exceed lower and even mid-level management at the same company).