Reason for different types on `by` steps

[Michael Pollmeier]

I don't understand the types on the `by` steps that take a function 
projection.

1) Shouldn't it be `Function<E, V>` for the function parameter in both 
cases?
2) What is the reason for constraining the function passed to the second 
one to `Element`?

without comparator:
<V> GraphTraversal<S, E> by(Function<V, Object>)

with comparator:
<V> GraphTraversal<S, E> by(Function<Element, V>, Comparator<V>)

(from GraphTraversal.java)

Cheers
Michael