It's not mandatory to have a surname wit yan or ian ending for Armenians. There are many Armenians with other Armenian surname endings (uni, ouni, ents, yants etc.) and without them in Armenain Diaspora, like Charles Aznavour (Aznavourian).
There are missing many famous Armenians like Charles Aznavour - a famous French-Armenian singer and actor, all members of System of a Down band (Serj Tankian, Daron Malakian, Shavo Odadjian, John Dolmayan), Aram Khachaturyan (famous musician), Ivan Ayvazovsky / Ayvazian (famous painter, marinist), Tigran Petrosyan (Chess Grandmaster, world champion), Levon Aronyan (Chess grandmaster), Garry Kasparov (Chess grandmaster, world champion), Arshil Gorky (artist), Viktor Hambardzumyan (famous astrophysicist), Kirk Kerkorian (one of the main figures in Las Vegas), Anastas Mikoyan (one of the main figures in soviet government, he had a huge influence in solving the Caribbean crisis), David Nalbandyan (famous tennis player) and many others not counting those who lived in ancient times or middle ages.