To say the truth, no one really owes anyone an apology for voting themselves, i mean its their money, their stake, their investment whether its quality or trash they are voting for themselves.
But personally I don't even like voting for myself and though my votes might not really amount to a tangible thing but i still don't think i would take pleasure in upvoting myself when i have good stake.
But all the same, its a personal thing to deal with and the system has no rules against self voting so anyone can do as he or she pleases with their upvotes