Why TSQL convert a function's result in one way and a character string to other way?

I try this command in SQL Server 2005 to obtain a MD5 from '123':

select SUBSTRING(sys.fn_sqlvarbasetostr(HASHBYTES('MD5',  '123' )), 3, 32) 

and I get this result:

202cb962ac59075b964b07152d234b70

I want to convert to binary format,

select 
   convert(varbinary(16), SUBSTRING(sys.fn_sqlvarbasetostr(HASHBYTES('MD5',  '123')), 3, 32)) 

And I get this result:

0x32003000320063006200390036003200

Why does this code:

select convert(varbinary(16), '202cb962ac59075b964b07152d234b70')

result in a different value?

0x32303263623936326163353930373562