Just pointing out that air intake tract is not exposed to any fuel (direct injection), so whatever you might put in the tank is not going to have any effect on this portion of the intake system. However, plenty of PCV oil vapors and similar in there that will cause a build up over time.
My understanding of the prevailing logic is, yes, if you look at the backside of the throttle body it's likely to have a layer of dark brown or black film, but unless it's causing drivability problems its best to leave it be (unintended consequences of damaging it or something else). I gather if the car is used mostly in stop and go driving, the build up will be greater. Quality oil and on time changes may help reduce the issue.
2017 MDX Advance SH-AWD, Modern Steel with Ebony
2016 Chevy SS, 6 speed manual