Yes, that's true. But if you run an email service that's based in Cupertino, what do you do when served with a lawful search warrant or wiretap order? Say "no," and be found in contempt of court and have all your servers carted away by some men in black so they can find the file they're looking for?
There are a few ways around this. One is not to permanently store warrant-worthy user data (Snapchat, Wickr, etc.). Another is end-to-end encryption (original version of Hushmail), though key distribution and UX become problems. A third is to move your servers to Switzerland, though then you get served with process from the Swiss authorities instead of FBIDHSDEAetc.
Apple has taken none of these steps. Assume our hypothetical Cupertino-based email service has not either. What do you do when the Feds show up with a lawful order?