The 520, 550 and 360 all have "vibration" sensors which are designed to put the remote to sleep after a certain period of inactivity (20 minutes??). They turn the LCD off to conserve battery power (not that the LCD uses much power anyway...)

This is different to the 880 and 890 and 720's tilt sensor, which is designed to light up the remote when you pick it up.

If the 520etc had tilt sensors to light up the remote it would drain the batteries in no time. The 880etc can do it because of the rechargeable battery.