Clearance Delivery can only get you an initial clearnace. and they are limited to 3000'
Departures then get you on climb to 3000 and move you as they need to and climb you when they can.
I was given an Amended 3000 clearance, and Dep then recleared me amended 1600, then after traffice was clear climb to flight plan alt.
its just a box arond they airport up to 3000' to get you in the air and then depaurtes move the traffic around as required. they then set you on track and give you to centre.
there isnt much confusion if you listen to the controller and read back what he says.