While underdeveloped countries are typically less well equipped to deal with natural disasters, and hence the consequences there are often worse, this doesn't by any means that major damage/high levels of mortality can't be seen in more economically developed ones (such as Italy). Some people have already spoken of the North/South divide in Italy, but in this instance it isn't all that relevant, as the earthquake occurred in the central region of the country which is relatively well-developed.
We need to remember that the circumstances of every earthquake are different. Firstly, magnitudes vary. On a simple level, if an earthquake of magnitude 3.1 occurred in a less developed area, i.e. Kashmir, and one of magnitude 7.5 occurred in somewhere like Kobe in Japan (comparatively well-developed), the results could well be worse in Kobe, regardless of its level of development. Magnitude is a logarithmic scale; 4 on the Richter scale isn't 1 unit higher than 3, it's 10. And it's 100 times larger than 2. So 7 is 10000 times as strong as 3. Equally, not all environments are the same; an earthquake striking a predominantly rural area is unlikely to do as much economic damage as in a large city, and similarly one in a densely populated area is almost definitely going to be more lethal.
Often it is developed countries who suffer quite acutely from natural disasters, purely because they're not used to them, and therefore don't have a great deal of infrastructure in place to deal with the effects. Here in the UK we're not close enough to any major plate boundaries to be that affected by earthquakes, but we only need to think about the minor ones which occurred in Kent not too long ago and the resultant panic, to realise that we too would probably not be in a position to cope particularly well with an earthquake of a similar scale here. And there's no doubt that we're a developed country.