"Fairness" has nothing to do with it. The goal is to build a reliable blockchain company that will provide great service to it's customers and a rate of return to its owners. Companies hire service providers to provide services, not as wealth distribution mechanism to "give everyone a chance to earn a little bit". Reliability, integrity and profitability are our design objectives. So any cost-effective implementation that reliably signs blocks correctly is acceptable.
For POW, POS, and DPOS systems large stakeholders control a disproportionately large portion of who signs the blocks unless the multitudes of small stakeholders are motivated to participate.
This generally does not happen for any of the systems because of a phenomenon known as
rational ignorance.
Rational ignorance occurs when the cost of educating oneself on an issue exceeds the potential benefit that the knowledge would provide. Ignorance about an issue is said to be "rational" when the cost of educating oneself about the issue sufficiently to make an informed decision can outweigh any potential benefit one could reasonably expect to gain from that decision, and so it would be irrational to waste time doing so. This has consequences for the quality of decisions made by large numbers of people, such as general elections, where the probability of any one vote changing the outcome is very small.
-- http://en.wikipedia.org/wiki/Rational_ignorance In a POW system, to make any impact a small hasher would need to remove herself from the hashing pool that she has had doing the signing for her (or at least make an independent decision about what software to run) - an act that requires becoming informed about that whole process. Then, the impact is felt only in the very rare event that lightning strikes that node and her software actually gets to sign a single block.
To continue having any effect, she needs to keep running her node and staying informed - both of which involve large continuing costs. The rational ignorance principle says she probably won't. Most holders of POW coins buy them rather than mining them and thus have no say at all.
In a POS system, to make any impact a small forger would need to remove herself from the leasing pool that had been doing the signing for her (or at least make an independent decision about what software to run) - an act that requires becoming informed about that whole process. Then, the impact is felt only in the very rare event that lightning strikes that node and her software actually gets to sign a single block. To continue having any effect,
she needs to keep running her node and staying informed - both of which involve continuing costs. The rational ignorance principle says she probably won't.
In a DPOS system, a small voter is still subject to the rational ignorance principle most of the time, but, when there is a problem, she can wake up and become informed on the source of the problem (probably by studying the forum debate and taking the advice from people there she trusts). Then, in a few clicks she can vote in a new slate of delegates, change who is running the system, and go about her business - w
ithout needing to sustain her efforts or incur any further costs. Her one time input takes place immediately and the problem is fixed.
With the other systems, the vigilance of the masses will eventually fade and the problem can reemerge.
With POW and POS, large players have absolute power over what software gets run every time they get a turn.
With DPOS, large players may have the final say, but they must pick from a pool of candidates that already have the most approval from everybody else. If the candidates preferred by the big players haven't done the reputation building work to attract enough voter attention from the masses to be close to getting elected, then those candidates are simply ineligible.
Bottom line is that the DPOS process only allows nodes that have reputations that are
sufficiently trusted by the general population and those reputations can be burned out of contention by a jury of their peers at the slightest perception of misbehavior.
Reputations are hard to earn and easy to burn.
And everybody has a fair say about whether they trust each and every candidate.
Thus DPOS is the only solution of the three discussed here, that has a way to ensure that all signing nodes have passed the threshold of generally acceptable reputations. This means that every single DPOS block is signed by someone with an
acceptable reputation to the owners of its tokens and never more than 1% of the blocks are signed by any one node.
That's all the typical small holder really cares about.