Must we use "have to"?

Ruth Walker has an intriguing post in her Verbal Energy blog for the Christian Science Monitor about the drift away from using the word "must" and the shift to "have to."

She makes a wonderul case, I think, for the brevity and power of this simple word. "Must" has not fallen out of use, but Walker notes a shift away from it that dismays me. "Have to" is simply using more words to say the same thing; perhaps I'm old fashioned, but in most cases short of dialog, I don't see much nuance of meaning between the two.

Fail to shorten "have to" to "must" in my class (in most cases), and you'll pick up a point on the lab.