The intensity of a magnetic field falls according to an inverse square law: in other words, the force of attraction is proportional to 1/d^2 (one over distance squared); that is, if you double the distance between them, the force will be 1/(2 squared), or one quarter of what it was at the previous separation.

I speculate that the magnets are mounted on a non-susceptible, non-magnetic back-plate, which are effectively acting as spacers, dramatically reducing the field intensity.

[EDIT ADDED: See the link from Evan two posts below, which explains this perfectly.]