I personnally see perfection (in anything other than very few scenarios) as a waste of time, especially something as cosmetic as drill (don't need to be perfect to understand the whole reacting to orders and all)
Aiming for perfection during training? Certainly. Demanding a perfect result? You'll spend 80% of your time chasing the last 20% of the results. Waste of time that you could spend broadening your knowledge and skills.
This is a propaganda pageant, a tool, put on for the world to see and admire. This has an important purpose to China and I agree with Loachman, this is probably all these people do for the State while they're in uniform. They have plenty of people and can afford to have just show performers on the payroll.
Could they be doing something better with their lives? Maybe... but the same could be said for all those professional athletes. They're at the top of their tier, doing what they do to the best of their ability. Could they have put those years of training and dedication into something more beneficial to society? Again, maybe... doesn't stop all the sports fans from ohhhing and ahhing while watching them to their thing.
Maybe those Chinese kids spend 80% of their time in uniform chasing that 20%. They seem, to my eyes, to have caught it nevertheless. Sure, you're right, good enough is usually good enough. I can still stand back and watch someone do something much better than I could ever hope to achieve and admire their work. (sure as frig, they look better than what's on display in the photo of our colour party, et al)