The magnets in the reader are extremely small. Magnetic field strength falls off rapidly based on the distance from the magnet. Magnets the size of the one in these devices are practically invisible to "magnetically sensitive" devices at distances greater than a couple of mm.
Secondly, neodymium magnets (neodymium-iron-boron or NIB) - as these almost certainly are - keep their magnetic strength very well, unlike the older Alnico magnets which naturally degrade without special handling.
NIB magnets almost certainly have a far longer lifetime than the device they've been embedded in. Case in point - my old Sony Librie has exactly the same kind of magnetic latch for the case as the new 505, and it's fine
www.dansdata.com is a good place to start looking for human readable info on NIB magnets.