I do not quite understand why people say "where are you headed?" instead of "where are you heading?"
Also,when replying to the above question, people say "I am heading home",for example. Why do not they say "I am headed home." Does this usage have anything to do with colloquialism?
thank you for taking time to read the questions.
I would call both forms (both the questions and the responses) equally possible. Googling gets us:
87,200 English pages for "he is headed"
141,000 English pages for "he is heading"
-- Not a significant difference in frequency, I think.
(In general, native respondents often answer using slightly different wording-- it is a method of checking the accuracy and completeness of the communication process.)