OK, the question "Can you walk off the ship without tipping and no one be the wiser?" Yes, you can. The real question is whether you should.
The suggested tips on
DCL total $12 per guest per day. That is divided among 4 people. SO, your room host would get $4 per day for each of you--$16 for a family of 4. For this, he/she will deliver and remove your luggage, clean your room daily, freshen the room with turn down service in the evening, get anything you need, and maintain the public areas near your room. Additional services from this individual would include things like recharging a motorized scooter for a handicapped guest, etc.
Your serving team works other venues at breakfast and lunch; the dining room tip on the last night represents the tips for ALL the meals you have eaten on the ship except Palo. Even though you are served by other people at breakfast and lunch, YOUR servers are serving other people. The tip is for ALL the meals during the cruise. Again, that total is $8 per day (the other $4 went to the room host), so $8 in tips for 3 meals per day, or less that $3 per meal. But wait, in the initial post, you said you tip $5 or $10 per meal! The difference is that you don't eat out 3 meals a day.
I'll echo some of the sentiments expressed here by others. If you can't afford the tips on a long cruise, perhaps you would be able to take a 3 or 4 day cruise and take care of those who have served you. Tipping is part of the cost of cruising. If the service isn't worthy of the tip, speak to the dining manager as soon as there is a problem so it can be resolved. Don't use the excuse of "bad" service to avoid paying those who have served you.