Only if you assume that all media is transmitted over HPG and none delivered via ship. And that ComStar broadcasts all media from its compounds for all to receive. Neither of which has been shown, though we do have accounts of having to wait months or even a year to get the latest episode of the Steinhearts.
I think I see why you're questioning what I was saying.
Granted: It may not be commonplace (or even ever mentioned in canon) that ComStar compounds are where all of a given planet's trideo broadcast towers are.
But that's besides the point. What IS being broadcast on the airwaves, whether from inside the ComStar compound or not, originally passed through the HPG network and was at some point transmitted from the ComStar HPG compound to whomever operates the broadcast tower(s) on the world in question. Unless of course the media in question was produced locally without any impact whatsoever from the interstellar economy. And no that's not snark. Surely some portion of the local media is 100% local. But any interstellar commercial enterprise, mass media included, requires ComStar. If not for the HPG transmission itself, then at least for use of the interstellar financial system.
On the other hand, we do have accounts of propaganda being spread on worlds via covert combat vehicles. Seems rather expensive when one could just send it via ComStar....
What the government does and what's commercially viable are not necessarily the same thing. An organization like the ISF or MIIO can afford such extravagances, esp when keeping ROM out of the loop happens to be a priority. Besides sometimes the propaganda in question isn't of a format that is compatable with HPG transmission. Enemy troops dug in defending a city are unlikely to be calling or visiting the onworld HPG for personal messages but they can't help but see leaflets airdropped on top of them.
OTOH commercial media enterprises that need to turn a profit can't afford to use distribution methods ridiculously slower and more expensive than HPG transmissions. The AFFS can afford to ship highly classified and non-perishable orders to units via JumpShip Pony Express, but the New Avalon Herald isn't going to ship its newspaper across the Inner Sphere in this way... news is perishable and it's just too much cheaper to go over the HPG net. And hypothetically if they pay ComStar to make its product available at every HPG compound across the Inner Sphere, then the only way the ISF or Maskirovka can keep its subversive influences away from their eta and servitors is to physically keep those plebes away from ComStar's HPG compound. Both physically AND remotely via whatever communications network technology the given planetary comms grid may have.
EDIT: In the case of something like trying to keep the New Avalon Herald from being picked up by an eta on the planet Annapolis: Rather than trying to tell ComStar what may or may not be broadcast into the Combine, they probably would find it most in their interest to enact a tax or tariff on such things. Price them out of what anyone but an elite can afford, and you can generally trust your elites. Or at the very least there's few enough elites you can watch them much more efficiently for signs of subversion. Besides, putting such tariffs can make it not in the New Avalon Herald's interests of profit to even ask ComStar in the first place to broadcast it to HPG stations inside the Combine, making House vs ComStar sex organ measuring contests moot.