One of my favorite questions.
(1) Yes, I also learned that "due" is an adjective, and
"because of" is a preposition.
The boss: Why are you late?
The employee: I arrived late due to trafffic problems.
I arrived late because of traffic problems.
My lateness is due (to traffic problems).
According to the rules, only the second and third sentences are
But, of course, few people would express themselves using the
(2) I think that you are correct: "due to" is now accepted as a
preposition along with "because of." I have no proof to offer, but
I can report the following:
At the best (in my opinion) adult ESL school in the United States,
the final examination in advanced classes accepts "due to" as a
preposition in sentences such as: I arrived late due to traffic
I think a few people are trying to keep "due to" an adjective, but they
have lost the battle, along with the few people who insist on saying
"It is I."
***** NOT a teacher *****
P. S. And I suspect the people who insist on "This secret is between
you and me" will lose to the growing numbers who say " ... between
you and I."
As you know, language is truly democratic. The majority rules.