While Ghengis' explanation gives one reason for installation of a stick pusher, it doesn't give the whole reason.
Stick pushers (and indeed also shakers) may be installed where the 'natural aerodynamic stall characteristics' of the aircraft are unacceptable and do not meet the regulatory requirements of sections 201, 203 and 207 of the relevant regs. They are an alternative to actually fixing whatever the underlying aerodynamic problem is.
Therefore, if there is no or insufficient natural airframe buffet or other 'stall warning' such that the requirements of section 207 cannot be met, one option available is to install an artificial stall warning system, or 'stick shaker'. This allows the onset of warning to be tailored to the configuration, and does not impose an aerodynamic penalty (which, for example, a stall strip on the leading edge might).
If the stall characteristics AT the natural stall are unacceptable with regard to the requirements of sections 201 and 203, then a stick pusher may be installed, set to fire at a lower angle of attack than where the natural stall occurs, in order that a relatively benign stall characteristic is obtained. Since the unacceptable characteristics may be a sudden wing drop or a pitch up, but not necessarily related to the tail vertical position, this may be required on any aircraft, depending on the detail wing design. In this case we would typically refer to this as a "pre [natural] stall pusher".
Finally, the T-tail/deep stall case may require a post-stall pusher i.e. set to fire AFTER the natural aerodynamic stall is acghieved, but intended to prevent overshoots of angle-of-attack in, for example, the dynam,ic stall case, which might cause a concern for a deep stall.
Without knowing the details, I'd suspect the 747 classics fall into the "pre stall pusher" case, likely as a result of a less-than-pleasant natural stall characteristic.