[Avodah] bracha on megilla

[Eli Turkel]

AFAIK there is no obligation to read any of the other megilot.
Shir Hashirim, Ruth, and Kohelet are just a minhag Ashkenaz.
Eicha is a universal minhag, but still just a minhag.  If you don't
read it, it's no big deal.  So how can you say "asher kidshanu
bemitzvotav vetzivanu"?  Who commanded you?  Not the Torah and not
Chazal.>>

it is a makhloket rishonim if we say a beracha on a minhag
for example on hallel on rosh chodesh. However, to my limited
knowledge this applies only on to minhagim mentioned in the gemara.
I don't think we ever say a beracha on a minhag that is not mentioned
in the gemara.
So I think that Zev is correct.

My question is the opposite. If one does read from a klaf why does
the Gra say one should say a beracha.
In other words what is the basis of the makhloket of whether to say
a beracha when it is read from a klaf and why is a klaf important?

-- 
Eli Turkel