If you read "The Little Things", you'll remember that I talked about the difference between individually wrapped slices of American cheese and sliced cheese that's not individually wrapped.
Wikipedia comes through to explain the difference:
The individually wrapped cheese slices are typically the least like natural cheese. These "slices" are actually individually poured onto each plastic wrapper and then set to emulsify. Small (e.g., 16 to 36 slice) blocks of presliced, but not individually-wrapped, American Cheese are also marketed, often with the branding "deluxe" or "old fashioned".
Viva, la difference! You can go to the linked article for the full story on American cheese.