Francois Tremblay makes a very accurate quote on why wages should be always equal.
Saying that inequality of capacities must lead to inequality of wages would only make sense if all work was the same, in which case the person with lower capacities should be paid more (for having to do a work more difficult than he can actually do) and the person with higher capacities should be paid less (for having to expand less effort for the same work). But in reality, the variety of work to be done is as great as the variety of capacities that exist in people’s natures. Since people can always find some work that suits them, or is at least proportional to their capacities, inequality of capacities coupled with a proportional inequality of work leads us back to equality of wages.
Francois has written an excellent short series of articles on the necessity of equality in society which make a solid case for what I always say in that you cannot have liberty without equality. Make sure you read part 1 and part 2 as well.