Ubuntu 10.04 LTS Desktop has reached EOL, while 10.04 LTS Server is still supported. 10.04 was the last LTS release which had different support length for the Desktop and Server versions. Since 12.04 every LTS release is supported for 5 years.
So the interesting question is what packages have became unsupported by the EOL of 10.04 LTS Desktop? You can look here where you will find a link to this list of still supported packages. As that list's first line confirms:
Lucid source packages not in this list are unsupported starting Apr 29, 2013
libyaml is not in that list. (How that list was decided I don't know.)
I feel too the discrepancy when it is said that the LTS Server is still supported, but only a few packages are truly supported. But this was well-known before, that the EOL of the Desktop release will cause a lot of packages to be no more supported. This discrepancy is likely one of the cause why Canonical switched to support every LTS release for 5 years, be it Desktop or Server.