Complimentary Premier Upgrades

Realistically, how common are they? From the way people on here complain, I didn't expect to have any luck. I only got Silver status in October and hadn't flown since until this week and I got upgraded on two out of three segments. Originally, it was booked as two direct flights but the night before coming back, I decided I wanted to sleep in and changed the flight, but that meant a layover. I was upgraded on the first segment (outbound) and on the last segment (second part of the return trip). Also the extra leg room on the segment I didn't get upgraded on was nice