Good point - I always thought the same thing, Ryanair's harp over Aer Lingus' shamrock! Yes, the harp is the official emblem, in fact I think the shamrock hasn't any official status.
Your point illustrates one other thing - Ryanair is the true flagship airline of this country!!
BTW, speaking of Irish airlines, Aer Lingus has been privatised (at last):
Ireland approves Aer Lingus privatization