I think winning in Australia will always be a bigger achievement for Asian sides. Australia has not only been the historical superpower of this sport but at home they are almost invincible, while the Proteas frequently shell tests at home not just against the 3 Asian sides but also against WI. England and Australia have won in SA often. In Australia only SA has delivered the goods consistently (last decade or so) while England caught them on the wrong foot once in the last 30 years (2010-11). The W/L stats justify that, Australia are a different level monster at home.
Another big issue I see is umpiring. What I say may sound like sour grapes but I do feel that under fair playing conditions both India and Pakistan should have broken the drought in Australia by now. Speaking for India I can say that we should have won at least a couple of series out of our '77-'78, '80-'81, '85-'86, '03-'04,'07-'08 tours. Those series were close draws/defeats only because of umpiring. I am sure Pakistan faced a similar problem as did Sri Lanka, during home umpire era Aussies knew exactly when to favor the home team, they had perfected the art of officiating to an exact science where only their side benefited. Even during neutral umpires era they get many decisions in their favor, not just howlers but in fact nearly all the marginal calls go in their favor. I can't pin point why this is happening in present era but from memory I can justify my stance.
In SA umpiring won't be an obstacle, I can see Asian teams winning there very soon. In fact I am sure once India gets a series win there, it will open the floodgates and we will enjoy many wins. England and NZ are bigger roadblocks for us in the future.
#Mamoon.
