Hello,
It has nothing to do with your explaination.
Like for all this kind of services, it the first
one to get a large number of users that will
become bigger and bigger. Other similar sites
won't be able to get enough new users to get
a part of the market. (People who use one
won't change to another especialy if it's
less popular).

Ebay was the first one in english, that's why
many people use it. Who would put something
on the english Yahoo when there is much less
people using it ?

Yahoo was the first one in Japan and many japanese
where using it before Ebay started to do it too.
For the same reason, those person won't change
to Ebay (especialy as they are not interested
to have non-japanese bidders) and new users
will go to the biggest site...

Cheers,
Yann Stettler