"I think they know what they're doing"
They know exactly what they're doing and part of this decision making
includes economic considerations (with some companies it isn't the
engineer's call to make). Even expensive components can be built with very
average part quality to stay within a pre determined budget target. The
builders working with these cost limitations are able to produce good
sounding and competitive products. Those components can be easily
elevated to very good and excellent levels with well chosen better parts.
It you're satisfied with the choices made in choosing parts then that's fine.
As Grannyring astutely pointed out, there's is often room for improvement
(sometimes significant) as an individual isn't hampered with the same cost
constraints for their specific audio system. As I noted before the issue of
part quality varies from one builder/ company to another. This is why many
companies will offer upgrade packages (better, caps, resistors,
transformers, tubes, wiring etc.). They recognize much better quality is
available but the cost puts it outside the price target of the standard level
components (for example V cap or ultra grade resistors options).
It's a personal choice and I believe options to improve/upgrade is a good
thing, your call.
Regards,