It's all about frame of reference, I think. If all you know is supermarket and Starbucks coffee, that's what you think coffee tastes like. People who claim to know what coffee is supposed to actually taste like tell us that coffee from those places is poor coffee. Finding a local or online roaster, a higher end market or going to a non-Starbucks independent coffee shop and trying their coffee to compare the taste will give you an idea of what the Starbucks haters think coffee should taste like.
Personally, I think Starbucks coffee is a bit bitter with a mild charred/burnt taste. When I go there it's usually for a cold drink or tea, if it's an emergency I'll grab coffee. I'm Canadian so the two chains that take up every corner are Starbucks or Tim Horton's, so my convenience choices are limited. 
I buy coffee that I have ground at my local market to brew at home since I've found a blend and a method that tastes ok to me. I can tell the difference between 'common' coffee and coffee made by people who like to drink good coffee, my parents drink Taster's Choice and my wife thinks all coffee tastes the same and why am I spending $20 on a bag of beans!?
Check some local grocery stores, some are beginning to stock some smaller sources. If they have a grinder in the store, pick up some beans and try brewing yourself a couple cups. Alot of stores have areas with various beans loose that you can fill a bag and grind them, getting charged for only as much as you grind.
.
