I think that if you go back and look at the China Airlines B747 accident report you’ll find that there wasn’t a vortex or turbulence encounter. If memory serves, the autopilot was engaged and one of the outboard engines failed. The flight crew either didn’t notice the failure or were so preoccupied with what caused the failure they didn’t recognize that the autopilot was trying its best to keep the airplane where it was supposed to be. When the autopilot ran out of capability, it disconnected and left the aircraft in a horrendous state of trim complicated by the asymmetrical thrust. From there it was most probably pilot control issues that exacerbated the problem.
As Miles suggested in his post, above, a clean airplane simply plugging along will usually not generate a huge vortex, and what there is generated will likely be more rotational than anything else. Additionally, unless the encounter is parallel with the aircraft leaving such a vortex, virtually all of those kinds of encounters would be cross-track and very short lived – but, again, as Miles suggested, it could be a very noticeable “bump.”
The B737 “rudder hard over” cases were a matter of not sufficiently understanding a phenomena known as “cross over speed,” and really had nothing to do with high speed or low speed stalls. In these B737 situations there was something that caused a significant rudder displacement when the aircraft was either descending to enter the traffic pattern or was already in the traffic pattern. With the roll tendency, naturally the pilots attempted to counter the roll with aileron input and attempted rudder input as well. It is believed that the crews were not aware of the fact that at slower speeds the rudder is significantly more powerful than the ailerons and there was simply insufficient aileron power to stop and reverse the effect of the displaced rudder. Had the crews accelerated the aircraft up to and past this “cross over speed,” where the ailerons become more effective and can be used to overpower the effects of a displaced rudder (even a rudder fully deflected), there is significant chance that the aircraft could have been saved – at least from that initial encounter.