You don't get concept of pipes exactly right. Pipe redirects standard output stream of command to a input stream of another command. Wget in other hand excepts URL as _parameter_, which is not a stream at all.
One way is to use xargs -command to translate:
echo "www.google.com" |xargs wget
or another example with multiple parameters:
ls | xargs echo
So xargs translates its standard input into its first parameters parameters and executes it.