Its something I wondered and googled this

which all seems somewhat familiar. Tenth post down is the claim that when you pout the magnets in opposition the magnetic fields are cancelled and he claims you can put such a device on top of a telly with no interference. 

Knowing nothing about magnets I have no idea of this is actually true.

Should be easy enough to test and that and the reduction of magetic field strength so dramatically over distance would explain why both Clearaudio and Pro-Ject have both used opposing magnet platters as well as YMOAN rather splendid looking DIY afair, with no apparent issue.