It is pretty much impossible to know failure rates this early. That 0.4% failure rates could be true at this moment when consoles have been out just few days. Actual failure rates can be known only after when consoles have been out for at least 6 months. Even around 99% of the initial Xbox 360 consoles didn't fail right after they were out of the box, it took usually minimum several months of use for failure. Heck, few people even knew about RROD during first couple months.
One thing you have to remember about failure rates... They can only get worse as time goes by, they never get better. You can have 0% failure rate within first day but 50% failure rate after 1 year. And pretty every electronics device have almost 100% failure rate after 20 years.
