Different Pronunciations of "OR" in "FORK&quo

Some Americans dictionaries, such as the American Heritage Dictionary and the Merriam Webster Dictionary, divide the pronunciation of "OR" into two kinds.

fork [fo:rk] ("faw + rk")
pork [pOurk] ("poa + rk")

short [sho:rt] ("shaw + rt")
sport [spOurt] ("spoa + rt")

But I don't realize the difference when I listen to Americans speak. And I can't find the regular pattern. So, why do American dictionaries of English make this rather "strange" distinction?

It might depend on what dialect of American English you are speaking. There may be some people who would make those distinctions. I don't, personally; all of those words would have the same vowel for me, with no distinctions between them.

It a rare distinction to make these days but some still do. The pattern is not quite regular but there is almost a pattern. This distinction is also still made in some British dialects.

http://en.wikipedia.org/wiki/English-language_vowel_changes_before_historic_r#Horse-hoarse_merger

Typo: "It is a rare distinction ..."

It's also known as the NORTH-FORCE merger so if the above link doesn't work try this one.

http://en.wikipedia.org/wiki/English-language_vowel_changes_before_historic_r#North-force_merger

The horse-hoarse distinction is actually preserved with some regularity in the traditional Eastern New England accent (although nowadays you only really hear it in middle aged or older people here). The distinction, when you hear it made in New England, is quite clear and noticeable. The "hoarse" class uses the centering diphthong [O@], whereas the "horse" class has merged into the "cot-caught" class and uses the quite open vowel [Q:]. Examples of pronunciations in the traditional dialect would be:

horse [hQ:s]
for [fQ:]
forty [fQ:4i]
warm [wQ:m]
corner [kQ:n@]
short [SQ:t]

hoarse [hO@s]
four [fO@]
pork [pO@k]
force [fO@s]
sport [spO@t]

Lazar, Are there any dialects that preserve both the horse-hoarse distinction and the toe-tow distinction? If so, would they also distinguish between ''coarse'' /kors/ and ''course'' /koUrs/ and thus have a three-way distinction between /Or/, /or/ and /oUr/?