Well, first message to list [hi list]!

    Ok, I took a bit of boot camp type
training and learned that if you yell
or scream or grunt loudly you can
hit harder. I think martial artists yell "he-YA!"
for this reason as well
    I believe this is related to the fact
that by yelling or whatever, you tighten
up your stomach muscles. This force
(or maybe just the extra force for the
scream) runs off into your hit, thus
making it a bit more effective.
    So, to add to what Lurker said yeah,
it is a method of concentration. It gives you
that extra "oomph" that blows you over 
the charts.
    I think that Anime/Manga has characters
call out their techniques as a way to take
that familiar "YA!!!" and multiply it, making it
seem that their actually putting more force
into their actual yell.
    Of course it may be that "Shinku-Haduken!"
is a special incantation that Ryu (of street fighter
fame) incorporated into his technique. So that,
to the character it's the actual words said that
make the power/technique/whatever happen.

Like always, this is in the eye of the beholder

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                            I NEED A SIG!!!
                                    - Hiro
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