It's a terrible comparison because of all the reasons above, if the white community decided Football was the game they'd have the financial and logisitcal systems/power in place to excel at it.
Secondly Football is a much simpler sport it's easier to play, understand and excel at, there is no requirement for specialist training as we see across the world with kids in poverty stricken areas such as Brazil excelling.
20 years is nothing
No the problem is why do they make that choice? Saying blacks prefer football is an inherently racist statement (NB: to be clear i am not calling you racist, i'm making a generalist statement), there are a multitude of reason behind why that decision is made, and it doesn't change the fact that a massive % of the countries population are not involved in the National sport in anyway.
Clearly you're having a pop at my use of the term institutionalised racism, even though you are using it in the wrong context, and of course it applies here, how on earth can it not were talking about a sport that takes athletes and rewards them on a level undreamt of in the poverty strciken parts of the country.
With all that's on offer to a top class rugby player I find the statement "they just prefer soccer' incredibly distasteful. It's like using crime statistics to say that a certain race is predisposed to certain crimes without taking into account the socio-economic impact on the society these criminals come from.
Regardles the Quota system is not racist, it's positive discrimination, that's a massive point of difference, and has been used across the world to redress the imbalance of many unfairly treated groups.
Is it right? Well no, as i've said i'm not saying Quota system is right, but if more had been done to demonstrate the development and opportunities afforded to the black population was the same as the white there would be no grounds for a quota system as everyone would be there on merit only.
And yes, it's linked to Economic development, which is why Rugby is so important within this discussion.