> I think it is easier to read,

I can subjectively disagree, but I'm confident that the complexity results in an objectively less comprehensible solution.

> the behavior is more obvious

Same response.

>  but the result is identical either way.

Maybe the outcome is, but the operation is more expensive. There is a reason that the "extend a plain object with another plain object" operation has a common implementation pattern. 

There's this as well http://jsperf.com/backward-merge-vs-forward-merge