Re: Why do people have trouble telling the difference between sodas?

I'm assuming that you are talking about comparison of similar flavors like 
Coke and Pepsi or Sprite and 7-Up.

There are many factors that go into the sensation of flavor.  Actually 
most "flavor" perceptions are really odor perceptions.  Volatiles enter 
your nasal passage at the back of your mouth and are sensed by the 
receptors in the nasal cavity.  These receptors are extremely sensitive to 
an enormous variety of aromas.  Have you had a cold recently?  If so, 
think about how the food tasted.  It was probably flat and kind of blah.  

Taste, as located in your mouth on your tongue, is limited to four 
sensations: salt, sour, sweet, bitter.  The specific points where these 
sensation lie are very localized.  You can verify this by using lemon 
juice, salt solution, sugar solution, and quinine water (available at any 
grocery store).  Dip a toothpick in the liquid and touch it on different 
parts of the tongue.

These factors can be easily confused by consumers (regular people) tasting 
the product because the identification of intensity of aroma notes isn't a 
common skill.  People can be trained to quantify the amount of flavor and 
aroma to a very high degree, showing both accuracy and consistency.  In 
your case they were trying to distinguish between very similar aroma 
profiles (cola, caramel, etc.) and very similar taste profiles (sweet, 
sour).  You probably would have had a more clear ability to distinguish if 
you had chose products of a similar category but formulated to be more 
distinct, i.e. pepsi/coke vs RC cola, Shasta cola, Double cola, Sam's, 
cola, etc.