Schmoogie and I did some math.
Since 1972, Samuel L. Jackson has been in 127 movies, or 3.4 per year.
William H. Macy has been in 115 movies since 1978. 3.7 movies per year.
Which means that William H. Macy is actually harder working than Samuel L. Jackson, and maintains my claim that Macy, rather than Jackson, has been in every movie ever made.
Check that -- Christopher Lee has been in 264 movies since 1948 (9 of which were Dracula movies -- and 6 of which are coming out in the next two years; we've begun to think that he really is Dracula), which is 4.3 movies per year. Making him the king, even though many of his roles have been kinda gimmicky.
(Edited to add...)