However, this does not negate my original comment. If departing IFR,
in the ABSENCE of such an instruction, be suspicious.

In my case (very similar to the OP's case) I was given departing
instructions as part of my clearance by ground. Its very rare to
receive those instructions again from tower so you wouldn't find it
odd if it wasn't repeated. I guess the ground and tower controllers
don't always coordinate as well as they should.

-robert