This has to have been asked before, but...
Hashed, rehashed, and then beaten like a dead horse...
Most recent thread is here:
http://www.orthodoxchristianity.net/forum/index.php/topic,24856.0.htmlIt contains some extraneous stuff and doesn't directly address the issue of why various jurisdictions have different practices but it does get into the underlying understanding and canonical rulings from which the variations flow so it might give you a start to narrow your focus. And like Fr. Anastasios I have to ask 'what canon of Nicea?'