[userbinator]

http://en.wikipedia.org/wiki/HTTP_ETag

(I know that servers can be configured not to send ETags or break caches by sending random ones every time, but this could reduce the data usage considerably since most of the responses would only include the headers.)

[rogerbinns]

The query parameters make each request different. Etags are not unique across the internet - just for a specific url. There is no way an etag would help here, unless the same request is made later. Even making a request with an Etag still means lots of headers returned which while not 10MB will add up to lots of traffic.