There's no pipelining, there's keep-alives though. It turns out pipelining is really bad for servers that talk to backend applications because it allows clients to a large number of requests to be handled and then close the connection. The server could have then sent all the requests to backends or needs to buffer them. In that case, even though the client has closed the connection, the server(s) still need to process all the requests.

In fact, there's been discussions on the httpbis list to downplay or remove HTTP pipelining since it's ambiguous and causes performance headaches.