"Cars" / "Doc Hollywood" (Or: How Pixar ripped off Neil Shulman)

Not being a big NASCAR fan, I didn't go and see Pixar's "Cars" when it came out. Last night, I finally did on DVD. It was nothing other than the "old" Michael Fox movie "Doc Hollywood" with animated cars instead of real humans. However, retreading old tires is nothing new (pun intended) but, when I watched the special features' "The Inspiration for Cars", nowhere does anyone tip their hat to writer/ producer Neil Shulman or his "Doc Hollywood" movie. Pixar's "Cars" director John Lasseter instead said, "we do our homework". The only homework he did was rent "Doc Hollywood" from his local video store. John then says, "In coming up with the idea for 'Cars', it is putting my two loves together." Apparently those two loves are "copy" and "cat".
If you cannot come up with an original idea yourself, why cannot writers fess up to what they're copying? I do not see anything wrong with being inspired by another's creation and giving it your own spin, but give credit where credit's due. And if it goes beyond being merely inspired to out-and-out copying all the major elements of the story, you should also give a share of the royalties. Oh, that last part is probably why John didn't fess up. But if he and other writers don't want to do that, why don't they then do what the writer of what they're ripping off did and actually think up something new?

Then again, did "Doc Hollywood" rip-off of a still older movie? If so, did Mr. Shulman tip his hat to that creator?
Scott