I've always felt that system lock was about preventing theft of the device data, not prevention of flipping the device itself. Like tons of other people, I have sensitive apps and data on my phone (banking, cloud services, etc), but unlike tons of people, I take great care to ensure logouts after I am done accessing said apps or data. Even so, a thief snatches my phone, I don't care what happens to the phone itself, so long as the data is safe.