The main reason I tend to use map is to signal to the reader of the code that this is an operation on a list not just on a set of values that are conveniently represented as an array.
In other words, to me, map and grep carry extra semantic value to future maintainers of the code. (In most cases, Wade-future does not really remember what Wade-past had in mind.<grin/>)
To me, your first example implies that we are transforming a list. The second implies we are transforming the elements of a list. Although the results are the same to the computer, to the programmer the meaning may be very different.