However, i read somewhere the actual hole in the hull is confirmed to be only 48.8m. I would think that if she did not sustain any other damages on the other side, she should have not tilted over. Am I wrong ?
It doesn't really matter how large the hole is. What matters is how many and which compartments are flooded. In this case it was apparently more than the ship could handle (2-3).
As for capsizing, if you have a partially-filled compartment, you'll get so-called free surface effect (water sloshing around), which greatly reduces the stability of the vessel. This has capsized ships (Herald of Free Enterprise, Estonia) in the past. Although in basic damage stability calculations the ruptured compartments are usually considered either lost buoyancy or extra mass, if the hole is small enough, they will act like partially-filled tanks instead and might capsize the ship e.g. during a turn.
This is also why the Costa Concordia capsized on the "wrong" side - the captain turned hard to port.
aren't these ships being built extremely high and thus compromising the balance point ? I mean..they seem to be like real inverted icebergs and therefore making it easier when losing the perfect balance for any reason, to tilt over ?
The superstructure of a modern cruise ship is relatively light. It is built of aluminium and high-strength steel, and contains large open spaces. On the other hand, the hull is thicker and contains heavy machinery and propulsion system components, fuel tanks etc. that keep the center of gravity down. Also, with ships it is not necessary to have the center of gravity below the center of buoyancy - what matters is the so-called metacentric height (you might want to google that, along with basics of ship stability), which must remain positive. However, if it's too large and the ship is "over-stable", it will be very uncomfortable for the passengers and the crew.
You can tilt an intact modern cruise ship quite a lot and it will still righten itself. I don't think the classic liners were considerably more stable.
I am just being very dramatic, but I am not even sure if a simulation like this exists on these projects or they are just pure calculations.
You can easily do extensive damage stability calculations with advanced ship design programs such as NAPA, although it might be that they only test if the ship passes the requirements (e.g. two compartments), not what would happen if three or four compartments were filled.
Anyway, with today's computer programs there is no need to make such tests in reality as long as the ship model corresponds to the actual ship.
Another thing i read about Concordia project is that it did not have a double hull. Most ships are said to have it if the navigation conditions or areas where the ship navigates demand so. Since I am not an expert and just wondering many things after this, if someone could explain, i would appreciate. Of course i can imagine that the cost involved would be very high that would not be feasible, but I would like to understand the opinion of someone that understands better.
All ships have double bottom, but AFAIK complete double hull is only mandatory for tankers, ro-ro ships and perhaps bulk carriers. I guess it is left out if there is otherwise not enough space inside the hull - the side compartments can take quite a lot of space and they can not really be used for anything because cruise ships don't need that much water ballast.
Double hulls are not very expensive, but it's more of a design issue.