Just to add on to what others have already said about the goals etc. It also boils down to the luck of the draw as far as how busy of a counter you get hired for in the first place.
My old store (although it was over a million a year counter) supposedly was one of the slower stores who never made it's goal since the beginning. The company saw this as a problem of the managers and employees so in the 5 and a half years I worked there, we had 6 managers and countless employees. The store was mainly in a business district with a few large hotels so we had mainly office workers and scattered tourist customers. It was nearly impossible to make goal there and you really had to try and hustle, quantity over quality. You have to make way above your goal or you have no hope to be transferred into a better store.
Some people were lucky enough to just hire into one of the busier stores. In my city, the suburban stores that were the only MAC counter close by did phenomenal business. All of the girls from those moved onto managers, freelancers, MAC freestanding, some to MAC Pro. In our area there were 5 stores within about 10 miles, including MAC Pro on Robertson.
It's like someone else said, if you know you have to sell $150 an hour and someone really indecisive who says they're not interested in buying today just wondering what would look good or one of your counters "chronic returners" (all counters have them!) walks up and wants a makeup application then you have to figure out a way to either high pressure force the indecisive person to buy loads of stuff or do a really quick application on the chronic returner just to get rid of them. It's very high stressful, and doesn't always result in the best customer scenario.
I have many times defended salespeople on many forums because people think the salespeople are just greedy or on comission (we weren't) but it's because of the companies goals you are sometimes forced to use your own judgement on who you think is likely to buy the most from you and of course sometimes you'll be wrong! Of course there are just some nasty miserable people who have NO business dealing with the public and no business behind a counter but those usually don't last long, cos if they piss off customers chances are they piss off the managers too.
In a dream world the nicest and sweetest people would also be the ones who buy the most, but of course it doesn't work out that way. Sometimes you spend a long time chatting to a customer cos you click with them, they might just be buying one pencil...or you might have to help someone who is nasty with you but they're buying a lot so you fake it till you make it. It's just unfortunate but a harsh reality of business and retail that you have to make that choice all of the time. You have to know how to be diplomatic above all.
As far as the best artists being the best salespeople..hmm, I'm biased because of the amazing people I worked with but I find them to not USUALLY be one in the same. The ones that I found to be incredible artists were sometimes on the quiet and introspective side, sometimes overly emotional. To be a good salesperson, you have to know how to be 'on' all of the time and 'act'. You drop your problems at the door and are bubbly, outgoing, and perky at all times. For some people, this is impossible and those people can't work in retail too log cos they don't enjoy the act. I've know some unbelievable artists who worked for MAC that have either gone on to do freelance for films, musicians, or gone into stuff like graphic arts and teaching cos retail makeup was too confining for them.
Some of the people who were great salespeople were cute, fun to talk to, had appealing style etc. and the reasons customers liked them was because of their enthusiasm, not because their makeup was always perfect.
Anyway sorry I'm writing a book
but to answer your original question..when I first started they told me there was a 7% turnover rate and when I started all of the employees had been with MAC over 5 years! That was in 1999. When I left, there were all new people and as I said countless managers. Most of the people that left, left the company for good. One of the guys I worked with had been with them ten years. He had 5 weeks paid vacation a year and made more money per hour than the counter manager. He went from making way above his goal to suddenly getting written up all of the time (even though his numbers were way higher than everyone else's). He has since been fired. So come to your own conclusions but it is a business, a retail business.
Some people think it's all fun and games and all playing with makeup or that it's a serious artistry job but I would say, judging from the hires before I left, that it's about 70% sales ability and about 30% artistry ability. They even said when they hire new people "WE hire for personality and train for skill" That's why I always encourage anyone who wants to work for MAC, even if they have no makeup experience to apply. As long as you are bubbly, REALLY good at sales, go in with the right 'look', you will probably get hired. You either have the stomach and the patience for retail sales or you don't. It's not for everyone.