a couple questions about convert()

Hello,

In a postgresql-9.3.1 database with UTF8 encoding I can do:

  select convert_from (E'\\x68656c6c6f', 'LATIN1');
   convert_from 
  --------------
   hello

But when I explicitly give the "to" encoding:

  select convert (E'\\x68656c6c6f', 'LATIN1', 'UTF8');
     convert    
  --------------
   \x68656c6c6f

Why does that second one give different results from the first? 

Second question: why is that none of the convert* functions are 
marked as immutable (thus preventing me from creating a functional 
index using them).  Surely if I convert \x68 to utf-8 the result
will *always* be "h", won't it?