The pull request data available at the url api.github.com/repos/<owner>/<repo_name>/pulls/<pull_number> has some extra information pertaining to things like review comments, commit comments etc, like the link and the number of such events for that pull request.
This is not the case with reviews. Neither the link (in the “_links” field) nor the count (towards the end of the data) is included for pull request reviews.
Though they are available at .…/pulls/<pull_number>/<reviews>, it seems to be a good idea to include the reviews information (link and count, atleast) in the original pull request data, just like review comments and commits.
It will improve efficiency for one, since the reviews for a pull request need not be fetched if it has no reviews (if the count for reviews is 0). The data also feels more complete this way. This would be a great feature to have in the GitHub API.