I'm not trying to downplay the role of amateur radio communications - I am a shortwave radio buff. But I've heard people on the news talk to survivors in Nepal using telephones. Apparently, there is some landline or satellite communications to Nepal available. Just saying.
That's the case in any disaster - some traditional communications are working, but not in all areas. Even Satellite has limited capacity, it works when a few hundred, maybe even a few thousand disaster workers are using it, but if a significant fraction of the population start using their satellite phone, the system is going to be overwhelmed. Ham Radio is also capacity constrained, but with many ham radio users being trained in disaster communications, organized health and welfare messages can still be sent out of the disaster area through the limited communication channels.
I was in Hawaii for the 2006 quake that knocked out power on Oahu. The landline system was nearly useless -- took 45 minutes to get a dialtone and even then, it was impossible to make a call (both locally and out of the area). I had DSL for about 45 minutes until my UPS battery ran out, but it was super slow. No voice cellular calls, but could send SMS within the same network (i.e. I could send to other AT&T customers, but not to Sprint and Verizon, and vice versa).
My landlord was worried about his elderly mother 15 miles away and a car accident plus a downed tree had blocked the only entrance/exit from our neighborhood so I ended up riding my bike to his Mom's house to check on her since he couldn't use the phone system to reach her. (turns out she was at her neighbor's house who was having a big BBQ to use up the meat from his fridge before it went bad)
And this was a relatively minor 6.7 earthquake 200 miles away that caused no real physical damage on Oahu, just knocked out the power on the Island. If it were a 7.0+ quake on Oahu, the situation would have been much worse.