Working retail myself, I kind of see both sides of the argument surrounding the OP's post.
On the one hand, yes. It sucks out loud to be used and abused with not even a shred of some kind of thanks. Which at this point I can say that money doesn't always count. I know people at my job who are the epitome of the "I do what you need me to do because you pay me and that's all I'm here for and thus I don't complain" types and when times have been tough even they have become uncomfortable and their morale is affected.
Morale does seem to be a dirty word these days in business. Keeping your work-force happy goes beyond paying them more. In fact I'd ALMOST venture to say that if your idea of keeping employees happy and keeping morale up is JUST giving everyone more money, you're missing a few things. Despite what it seems like, life doesn't revolve around just money, at least for most people. If you have a small workforce that are stuck doing the job of a larger one and they're really being pushed to their limits, it's best to make sure that the creature-comforts are at least intact for them. It takes the edge off of busting your arse if you see that, while you may not get paid the most, your employer is taking care of you/appreciating you in SOME way that at least seems sincere. Sincerity, either actual or the appearance of it, is important, as is consistency. Not escalation, but consistency. Workers want to feel valued in some fashion, regardless of what they do. There are ways to do that that cost little to even no money at all (words are cheap, folks. A simple "thank you" can go a long way if the employee can see you are genuinely thankful for their efforts.)
On the flip-side: many times employees fail to understand that simple clause of "other duties as assigned". It means you do whatever needs to be done, plain and simple. Yes, that sucks and it's kind of an unfair clause, but everyone sticking only to their job descriptions causes just as much pain. It fosters resentment and misunderstandings due to the grass always being greener someplace else. It can also create problems in terms of customer service and sales. Like it or not, Customers DO sign your paycheck in a manner of speaking. Helping them out is in your best interests. I can't count how many customers have been pissed off and left where I work because someone got on their high-horse about what their responsibilities or their department is. That's money out of your pocket and mine, bub. Be as snippy as you like but don't come crying to me when none of us have a job.
Also, while some people are piss-poor managers and some are great managers, they are all people. Furthermore ALL of them tend to have to spend a large amount of their time fixing messes and dealing with angry customers that you SO KINDLY threw them under the bus to. That's the crappy part about THEIR job: they are equal parts babysitter, taskmaster, and complaint department. None of which are fun to be if you're an even halfway decent human being. Thus while you may be pissed about all the extra work you have to do, being confrontational and standoffish doesn't help your case unless you do it rarely. If there's one thing that many managers learn to be immune to it's rage. Logic, kind requests, and other non-rage approaches tend to get them to listen. For example: I myself had a stretch of a month or so of cleaning bathrooms, a task which is almost universally hated where I work. Managers simply kept picking me for it. It wasn't until after that month went by that I went to my boss and said: "hey, would it be possible for someone ELSE to clean these bathrooms once in awhile? I don't mind doing it every so often, but the past dozen times I've closed I've had to do it. Is it possible for someone else to deal with it every now and again?"
Surprisingly, the reply was: "You've done it that many times?! Wow...I guess we've all been picking on you! Sorry about that! We'll make it more fair, I promise."
After that, yes. Things were more fair. Other people went in and raged about being told to clean bathrooms, and guess what they were met with? indifference and the "you don't like it? there's the door" bit. Treating managers like human beings along with backing up your words with actions yields results. Anger and an air of entitlement gets you nothing. Picking your battles helps as well. The more you complain, the less weight your complaints have because, well, you're ALWAYS complaining about something.
Of course, that doesn't work with EVERY business and EVERY manager. Some people or businesses are just well and truly awful. But I've been surprised at how many times simply sitting down and having a civil discussion with my bosses has yielded, if not the results I wanted, steps towards it.