I don't see that much difference between the distribution of votes for either the 75 or the 300 word challenges. They both usually show a widespread signature. whether the voter has 1 or 3 votes to bestow.
However, I don't think it has much to do with a general, overall excellent quality of the stories. Yes, the quality is excellent, but in many cases people vote for their favourite story, stories they
like, for various reasons. Not necessarily what they call the
best story. I mean, can anybody give me the definition of the best story, apart from "I liked it best", "It spoke to me", "I like the twist at the end", or "It made me laugh"?
At best, 'best' means a story that shows characteristics that approach
my preferences of what makes a good story. Nothing technical, if such a thing exists.
Tastes differ. And therefor, so do the votes.
As an example, take a look at the current tie-break. Neither of the 2 stories got a mention from me. Not because they were bad, but simply because there were other stories that I (personally) found better.
The advantage of three votes is that the winning entry will end up a much larger share of the vote, the disadvantage being that it may be no-one's first choice.
Is it a disadvantage? If 5 people find story 1 'the best', 10 persons vote for story 2 as 'second best', and 30 voters mention story 3 as their third option, what would be the better story? The story with (limited) 'the best' marks or the story with the most votes? Mind you, in most cases you don't know what voters consider their nrs 1, 2 and 3. And quite often choosing between stories is hard because their all good, but for different reasons.
My 2cts.