I really need the ability to accept or reject files as a whole.

Consider reviews with lots of files, or reviews with complex or very interrelated code spread among multiple files. The reviewer is likely to jump back and forth between multiple files to ensure the solution that is being reviews is solid. Once a reviewer has determined that the file is acceptable, they need to be able to mark it as such so that as they continue on they can keep track of that. Otherwise, if they get interrupted during the review (again consider large reviews that likely will be completed over the course of a couple different chunks of time) they are forced to basically start over because they've lost the context of what has already been reviewed AND accepted.