Actually, it's funny, that is a clever idea and it's exactly why key-plus-ring is popular: Aesthetics. Specifically, minimalism. Less stuff. Less bulk.
It's not desirable in everything, but here is an example of your handleless tea cup:
http://www.jollygoodtea.com/ProdImages/206-050green-tea-cup....
I think it's pretty, but I do like classical East Asian minimalism and modern minimalism.
But other designs can be nice too - highly functional and somewhat spartan can be great. I also like really grandiose Victorian stuff, like a big sturdy wooden desk with a globe on top of it and paintings and brass fittings and craziness everywhere.
So minimalism/less stuff isn't the only way, but enough people do that this will sell well. I gave myself a light kick for not thinking of it first.
Can't see that. Imagine getting rid of the regular key-ring and just attaching a bunch of these new-style keys to one another. See what an unwieldy blob that gives?
And about bulk. Excuse me but what kind of key-ring do you carry? Mine weighs all of half a gram or less...