This doesn't work for:

deepCompare({name: 'blah'}, null);

typeoff null returns 'object', so it will pass the third line, next Object.keys(null) will throw an error.

In my opinion it is not just preference. At least not when you try to write code which most clearly conveys what it is supposed to do. In this case we want to know if every element in an array is an integer. Afterwards, it's just micro optimization I'd say. (I.e. if you have an every implementation that continues after the predicate returns false, than fix the implementation in stead of working around).

Excellent kata, totally uplives it's goal.