Hi,
A lot of distro's had/have their own/different naming schema. The last few years I see a tendency toward wanting to conform to standards, but they also want to be backward compatible. That's why the 'double' inet.d is there and all the links exist.
'The standard recommends' ( not starting a flame here
) the /etc/rc.d/init.d structure, I believe that /etc/init.d is RH's 'old' structure.
Hope this helps.