client.println() is sending data to a specific client.

server.println() is sending data to every client that is connected to the server.

Also, i believe that the arduino keeps sending data to the client instead of stopping the request. You should have some javascript that updates the value say... every 5 seconds or so... Or you could have a

<meta http-equiv="refresh" content="5">

inside the part which would tell the browser to refresh the page every 5 seconds instead of using the header

client.println() is sending data to a specific client.

server.println() is sending data to every client that is connected to the server.

Also, i believe that the arduino keeps sending data to the client instead of stopping the request. You should have some javascript that updates the value say... every 5 seconds or so... Or you could have a

<meta http-equiv="refresh" content="5">

inside the part which would tell the browser to refresh the page every 5 seconds instead of using the header

See http://tentencraft.net/demo1.php vs http://tentencraft.net/demo2.php