Work ethic rewarded?!?

Have you ever noticed in the workforce that seems that those who do not do their jobs properly get rewarded and those who do their jobs well just get more stuff assigned to them? I have a story that will refresh your memory if you have forgotten.

Recently, a coworker (who we'll call Slacker), who had had two previous incidents of reprimand, was to have her final written reprimand. This was to be done last Wednesday. My boss was coming in from her vacation to speak with this individual. That morning, Slacker was to open the store. Instead of opening, she called another coworker 10 minutes before we were to open asking if he could come in and if he would put her in for two personal days - two unapproved personal days, two unavailable personal days. She was taking an unauthorized vacation, taking advantage of the long weekend.
What would you do in my boss' shoes? Well, as she told us today, after speaking with Slacker, she allowed her to take tomorrow, Thurs., Fri. and Monday off as "sick days" (normally you need a doctor's note to take 3 or more days off as sick days). Where does this bother me? Well, I'm already doing the work of another coworker who was sent out of town for a week, and now I'll have to do Slacker's job as well, one which coincidentally was going to be rather tedious this week since we expected about 80,000 worth of books to come into the store and have a end of summer session rush. Lucky me I get to wear three hats this week.
My boss' comment? "Well, you can come in on Friday (we don't work Fridays in the summer) to get your paperwork done". Oh lucky me, don't I feel special.