When I last used the the Places API (6 months ago) it would only return the 5 "most helpful" reviews. I can't find in the documentation and verbiage to suggest this was changed to the latest reviews.
https://developers.google.com/places/documentation/details#PlaceDetailsResults
Update: Currently users are requesting a change to the sorting order via the Google Places API feature requests, changing from "most helpful" to latest- http://code.google.com/p/gmaps-api-issues/issues/detail?id=4258&q=apitype%3APlacesAPI%20type%3AEnhancement%20reviews&sort=-stars&colspec=ID%20Type%20Status%20Introduced%20Fixed%20Summary%20Internal%20Stars