a) It's correct to use the term "actor" for males and females
b) It's an international phenomenon
c) For origins and purpose of the change, see the Wikipedia entry for actor:
The word actor refers to a person who acts regardless of gender, while actress refers specifically to a female person who acts; therefore a female can be referred to by either term. The Oxford English Dictionary states that originally "actor" was used for both sexes. The English word actress does not derive from the Latin actrix, probably not even by way of French actrice; according to the Oxford English Dictionary, actress was "probably formed independently" in English. As actress is a specifically feminine word, some groups assert that the word is sexist. Gender-neutral usage of actor has re-emerged in modern English, especially when referring to male and female performers collectively, but actress remains the common term used in major acting awards given to female recipients and is common in general usage.