is exactly what AFMA is designed to correct. How many of those 400 petition signers know what AFMA is, and have properly calibrated their lenses? I suspect the number of petitioin signers with a camera that's actually defective is much smaller than 400, as many of those people quite likely read about it on the Internet, and decided they have a problem unit despite not checking appropriately. So, you have a few people in Germany with cameras that are actually defective…and it's the second best selling dSLR in the country according to Amazon.
In this scenario, you're presuming things you have no way to check upon unless you work for Canon, or have the skills of a great prophet.
One person could make the case this online noise means only a few duds exist, while another could claim the noise represents a much larger number, like statistical polling does.
Either way is presumptuous unless you have the actual raw data. The only way for non-Canon employees to gauge product satisfaction is from their peers ,or, as you say below, a product recall. But as you and I both know, mega-corporations are not exactly models of self-regulation.
Sure, it's unfortunate that some people get defective products, but as I stated, defective units are unavoidable in any mass-produced item. In the case of the 70D, the camera came out less than one year ago, meaning everyone who owns one still has warranty coverage provided by Canon.
Unfortunately, that means nothing. My 7D had the dreaded focus issue. I shall not go into the details here.