friends_timeline.json returns several types of statuses. (status, retweet, follow...)
A friends timeline fetch retrieves 20 statuses at a time. The FE then filters out everything from that fetch to only include "status" type events. So the result is that you asked for 20 statuses but you get less than 20 if those other events are in the results returned. When I login, it displays 3~5 statuses sometimes in friends timeline. rarely, no status.
Edited by Jasper Lingers