Erm, yes, Manchester is a regional airport...it's outside of London and doesn't have a major hub airline, so I would rather consider it a regional airport.
And I do not think it strange that Liverpool starts with more flights to Dubrovnik than Manchester to Athens... Dubrovnik is a highly popular tourist route, where as Athens is not a large tourist market in its own right (compared to many other similar sized cities in Europe). As Olympic is already in a vulnerable financial position, I bet EZ are confident they can wipe them off this secondary route through a slow expansion, rather than an all-out assault (with all the costs that this would entail)...have more faith in the EZ route planning departments!