Writing well at a 4th grade level != writing like a 4th grader, and I suspect it is equally difficult for science/eng majors and humanities majors. While it may not be necessary when writing for pg et al, remember that the average American reads at a 7th to 8th grade level[0] and that "for recreation, people read texts that are two grades below their actual reading level"[1]. In other words, you might be able to sell your startup idea to pg at a higher reading level, but you shouldn't count on selling it to consumers (and dare I say even investors/businesses?) that way.

[0] http://en.wikipedia.org/wiki/Literacy_in_the_United_States

[1] http://en.wikipedia.org/wiki/Readability