So to the OP's question, there is likely a kernel of truth in the statement. In the mass market that he serves, that is liekly the case. I would guess that every major manufacturer has a basic line circuit, power supply design, volume/remote ciruit etc. A simple integrated amp is those sans the additional doo-dads like dolby surround etc.
But what's an integrated amp at its core? Answer: a preamp and a power amp in once chassis, with significant savings, and no wires. After decades of contract design and input in high end I'm back to designing my own stuff (maybe for market if the supply chain ever un-knots) and guess what I'm starting with? Yup, and integrated. It just makes sense if convenience and cost are a factor at all. So in theory, IMO, its the perfect package. Further integration (e.g.: on board DAC) comes with tome packaging and power trade offs that i dont wish to make, but combining the power and pre sections is quite manageable (biggest issue: controlling power supply noise from the big honking power output stage - and i figured out how to do that).
Remember also that at best buy the models are typically made specifically for big box sale and are not the "reference" series others carry.