As per Captains brief - Cabin crew are there for your comfort and PRIMARILY your safety. They are not there to check on you every hour for 10,11,12+ hours in case your drink has run out. If you want something, ASK for it. Or, as Mashie said (but a lot more eloquently) Get off your arse and go and get it!
I never ceased to be amazed by people who think because they(or their employer) have paid for a flight they should be waited on hand and foot.