1. A method in a near end network optimizer of a client device for supporting a delta compression technique for reducing network resource transmission size, wherein the near end network optimizer is included in the client device and coupled with a far end network optimizer included in a server, the method comprising: generating at the client device, a first request for a network resource; responsive to determining that a version of the network resource is not stored in the near end network optimizer of the client device, transmitting the first request for the network resource to the far end network optimizer; receiving, from the far end network optimizer, a first response that includes the requested network resource, wherein the first response also includes a directive that a cached version of the requested network resource is not to be used to respond to a future request for that requested network resource without successful revalidation with an origin server for the requested network resource; storing, in the near end network optimizer of the client device, the requested network resource as a first version of the network resource regardless that the first response included the directive; generating, at the client device, a second request for the network resource; responsive to determining that the first version of the network resource is stored in the near end network optimizer of the client device, transmitting a third request for the network resource to the far end network optimizer, the third request including a first version identifier that identifies the first version of the network resource stored in the near end network optimizer; receiving, from the far end network optimizer, a second response that includes a differences file that specifies a set of one or more differences between the first version of the network resource stored in the near end network optimizer of the client device with a most current version of the network resource, wherein the second response does not include the entire network resource regardless of the directive associated with the first version of the network resource; and applying the set of differences specified in the differences file to the version of the network resource stored in the near end network optimizer of the client device to generate an updated version of the requested network resource in response to the second request generated at the client device.