The number 30 is completely irrelevant in this case. This isn't a sample that is supposed to be indicative of some fact about a population. This is asking people their opinions about balance in a game. If you ask one smart person, this is potentially as revealing as asking 1,000. Given, having more people is less prone to bias, but acting like this is related to what you learned in stats is just wrong.
Barring extreme circumstances any poll will be related to what I learned in stats class.
I doubt you understand the concept. Unless the goal of the tier list is to learn the opinion of the tier list from a few random members of the mbr as opposed to the mbr as a whole, then asking 12 members out of that population is useless.
And lol about asking one smart person. Looks like I am going to have to explain skew to you.
Let's say 1 person with a few peculiar views(for example Puff as 1 and Marth as a mid tier) votes in this. Even with the other 11 votes with more conventional views such as Fox at #1 and Marth as high tier, the mean(average) calculation will be moved away from the convention because of this 1 data point. Even in a group as small as 12 this isn't such a big deal, but what happens if more than one person with unconventional views vote? What if it's 4 or 5 or 6 with peculiar votes? Then what happens is that the curve of the data points gets skewed so badly from what it should be because nearly half of the votes are strange and not representative of the top players because some idiots decide that having 12 data points would be enough.
I know I'm not the best teacher but I hope you get the point now.
If however
not dealing with random sampling here, so what shriek said
edit: whether you agree w/polling "experts" is largely a different issue i think. no one has claimed that the distribution of mbr opinions on the tier list is "normal". kind of a weird thing to say anyway unless the question is something like "what % of players think x is the best character" or you are looking at individual permutations of tier lists as outcomes and saying the distribution of these lists is normal. and in the latter case we actually have many reasons to believe that a large scale poll of tier lists would not have normal results b/c we would expect more than one mode (look at how long this thread is), and heavy skew (it is widely recognized that a handful of characters are much better than others)
The point of a distribution being normal isn't to say it's normal. It's so that all related coefficients, measures of variance, confidence thresholds, etc provide a useful calculation. That is all lost if we do something as stupid as making the tier list composed of 12 sample points. And as mentioned in my response to Shriek above it leaves the tier list open to rather frightening data skew possibilities.