Well, you're close. You're only off by about 900 million. Here's a link that will tell you that Bush has increased the amount of US from 350 million to 950 million. The 50 million number you're quoting was stated about 4 hours after the event and before anyone had any idea as to the extent of the disaster.
http://www.iht.com/articles/2005/02/10/news/tsunami.html
"WASHINGTON President George W. Bush has pledged almost to triple the U.S. contribution for countries devastated by the tsunami, bringing the total to nearly 950 million."
I find it ironic that you would mention "Desperate Housewives" The network, ABC, that airs that show did in fact do a two hour primetime special on the tsunami. While it wasn't a telethon they did start each segment and go to each break with a public service announcement letting people know where and how they could contribute funds to help the relief effort. The other two main US networks, NBC & CBS, also aired specials with the same type format requesting donations to relief agencies. So, telethons? No. Effective? Yes. According the Red Cross they collected $15,745,701.06 due to events such as these.