Well, yeah, but the point is that compression can cause the leakage of information through timing that would not otherwise have leaked.
An interesting paper on using padding to obscure length: http://cihangir.forgottenlance.com/papers/lengthhiding-corre...
As for compress. My understanding is that the inscurity has nothing much to do with timing, and everything to do with giving an attacker some "known" plaintext they can use Bayesian (Turing?) analysis against to shorten the key space.
Problem with compress is the protocol headers give you a known part at the start of every message. Which you can then very quickly test keys against rainbow tables or other statistical means.
The best solution i know for this is to compress, then xor with a stream cipher then run into a decent block cipher.
The "compress after encrypt" is a trick question. If your data doesnt get bigger after that your encryption implementation is royally broken.
But you definately don't want every "plaintext" message starting with "..gzip".