American Cheese v Cheddar Cheese

Does American Cheese work as a viable substitute for Cheddar Cheese?  Those who frequent Potbelly seem to think so.  About a year ago, Potbelly switched from using American to Cheddar cheese.  When people ask if they can get American Cheese on their sandwich or salad, I deliver the devastating news that we in fact don't have American Cheese.  When I tell them what cheeses we do have, they are almost always content to have Cheddar cheese instead.  I cannot help but ask if there is *anything* that these two cheeses have in common, aside from color.

A quick Wikipedia search concludes that American cheese used to be made of cheddar but now is made from a mixture of a few ingredients like milk, whey, milkfat, milk protein concentrate, whey protein concentrate and sald (Wiki).  Doesn't sound too appealing.  Some people even go so far as to say that American Cheese is not even cheese.  What about cheddar?  The same simple search shows that Cheddar originated in the village of Cheddar in England.  Now this is what I'm talking about!  How can anyone think that these two are even close to the same thing?  A third search led me to a Yahoo! Answers page about the differences between the two.  There are some great responses.  I especially like the response from Michael.  He says, "Some American Cheese 'makers' add so many items to their American Cheeses that they can no longer call it 'cheese'.  In its place we get items like Cheeze Whiz and Velveeta.  These products are sold as 'cheese food', 'cheese spread', or 'cheese product', depending primarily on the amount of cheese, moisture, and milk fat present in the final product".

I interacted with a lady who, upon hearing the news that I didn't have American Cheese, shook her head at me and just left!  What an inspiration!  Thanks to her for not accepting a substitute for a cheese substitute.