They are not built in the same factory. While they are owned by the same holding company, they are still entirely separate companies that do not operate in conjunction with each other.
ALL major manufacturers have had QC issues at one time or another, especially when introducing new models, so you take pretty much the same risk no matter what manufacturer you choose.
I've owned many Marantz receivers and I have had an issue with one integrated amp, but it was quickly taken care of by the dealer who sold it to me.