[This is more evidence historically that Salieri and Mozart were friendly and even composed a piece together. The events that inspired Amadeus was that when Mozart was dying he wrote in a letter that he was positive he had been poisoned. After Mozart died, Salieri's compositions started to decline in popularity, and then he claimed that he was the one that poisoned Mozart. Although no one can be sure what actually did happen back then, it is much more likely that Salieri saw his compositions declining and ,as a last ditch effort to preserve his name, claimed that he killed Mozart causing his name to be attach to Mozart's forever in history. It is also more likely that Mozart succumbed to his life style choices, choosing to spend more time parting than working. However, Peter Shaffer did present a very interesting spin on what could have happened in his play, and did get Mozart's personality down to a T based off of letters he had written to his sister.
In other words, the Mozart presented in Amadeus was probably very similar to the real life Mozart, but take the story with a grain of salt.