I could be mistaken, but barring the issue of interference, doesn't PLT make sense in country where getting an ADSL line installed could take months? I mean powerlines can be found on even the most remote little farm.
There is another major issue that has been mentioned to me by a number of electrical engineers:-
Many electricity networks in ZA are extremely old and badly maintained (don't think I need to explain myself there

). As a result there are many cable joints that are heavily corroded. These joints tend to act like low pass filters which is not problem a problem for the 50 Hz wave that they are carrying. As soon as you overlay the high frequency carrier onto the line it gets heavily attenuated and the coverage is rather pathetic.
There are probably other issues as well but basically it comes down to the electrical properties of a line that is designed for something completely different from what they are wanting to achieve. The amount of engineering that will be required to hack a power line into a telecoms line is not trivial - no matter how much the marketing people try to hype it.