There are tons of stories and alternate worlds in literature that are very exciting without any races of non-human protagonists. Conan isn't bland. The Iliad and Oddessey aren't bland. Le Morte D'Arthur isn't bland. Perhaps part of the problem is that most published campaign settings devote insufficient time toward making different human groups distinct, intriguing, and immersive from a cultural perspective?
Personally, it's my thoery that demi-humans are just kind of a shorthand tool that allow you to easily apply stereotypes without having to delve into the complexities of human psyche and culture. Really, when it comes down to it aren't they all just metaphors for certain aspects of human behavior? IMO every trait that demi-humans have is just there to provide a caricature of humanity -- a lens with which to view human behavior from a different perspective.
However, the source material, humanity itself, still remains rich and complex, filled with every possible trait, motivation, and ideal. I would argue that if you remove all of the demi-humans, you don't lose a single thing. Instead, it remains there in it's primal and chaotic form, waiting for you to pull what you want from it and shape it to your needs.
Bland? No way!
(It is possible though 
) It was an all anthro; awesome ideas, lack of insight. The players were practically giddy over the idea. Sorry if i jump around a lot(first reply EVER)
