The joke was a reference to that pop culture idea which pointed out that if the infinite monkeys thing is real, there should also necessarily be products that are very close to great works but not quite right.
Yes, but the additional joke is that a room full of keyboard-mashing monkeys haven't only produced random nonsense, but have almost produced something well-crafted - much like with Cow Tools.
There's an additional layer to the Simpsons joke, with Burns dismissing what's really an incredible result (almost the opening line from A Tale of Two Cities) as useless just because of one small error. The Cow Tools equivalent might a farmer holding the saw, saying "This isn't even sharp."
Given that the monkey is sitting there smoking a cigarette, clearly stressed out, chained to the typewriter, I wonder if there's also a third or fourth layer to the Simpsons joke where the monkey represents the scriptwriter and Burns represents Fox. The equivalent for Cow Tools would be, er, Cow Comics, and it's just XKCD art quality comics on the Cow's table, and the farmer complains that the drawings aren't very good.
It is the infinite monkey theorem from the late 19th and early 20th century.