Well if you look into this sentence

Premises is greater number of newspapers are sold in Town S than in Town T
Conclusion is that citizens of Town S are better informed about major world events than are the citizens of Town T.

Now First of all we need to carefully see that it is an EXCEPT question, so all but one will be true.

Now down to explanation:

Assumption 1: Town S has a larger population than Town T.
Say Town S has population of 100000 and new paper purchase is 90000. Town T has population of 10000 and news paper purchased is 8000. If you see on percentage point then more people in town T is reading news paper than the people reading it in S. So it does weaken the conclusion.


Assumption 2: Most citizens of Town T are work in Town S and buy their newspapers there.
Say both Say Town S & T has population of 100000. However Town T people mostly work at town S so they buy newspaper from there. May Be only 20000 of S citizen buying newspaper in S however remaining 50000 newspaper were purchased by citizen's of town T when they are in S. So this also weakens the conclustion.

Assumption 3: The average citizen of Town S spends less time reading newspapers than does the average citizen of Town T.
If average citizen of Town S are spending less time reading newspaper then they are not better informated. So this also weakens the conclustion.

Assumtion 4: A weekly newspaper restricted to the coverage of local events is published in Town S.
If only local events are covered only for town S, and not for town T. Then obviously citizen's of town T will buy few newspapers. So this also weakens the conclustion.

Assumption 5:The average newsstand price of newspapers sold in Town S is lower than the average price of newspapers sold in Town T.
Logically thinking newspaper prices does not vary by huge margins. Moreover average price is not indicative of overall range of prices. So although this may weaken the conclusion but it will be least factor to count it.

As in GMAT you are supposed to pick the best one out so I will go with the E.

Your looking for the answer that does NOT weaken the conclusion, which is:

The citizens of Town S are better informed about major world events than are the citizens of Town T.

So we need the answer that tells us that the people of Town S read more about world events than Town T.

E) is the only one that does this by telling us that the newspapers are cheaper in Town S giving the people more of an incentive to purchase and read about world events.