No it isn't. Submarines can be neutrally buoyant at any depth because they have the ability to control their density. The fact that water is slightly compressible has no effect on submarines' operation.
No, WalterBright wasn't the one who worded it badly. Seems you still need to think about it some more: How does adjusting the density of the submarine help change its neutral-buoyancy depth... Unless the density of the surrounding water also varies with the depth? And how does that vary, unless water actually is (albeit very slightly, I imagine) compressible?
