You, my friend, are unfortunately in error.
Both W5UDX, Greg and WZ5Q are using Voodoo Modified TS-950sdx. Greg was recorded on 75m with a 40 over S9 Signal on the receiver, & WZ5Q was recorded using the TX Monitor on the rig. The recorded Audio came from the headphone jack on the TS-950SDX, through a Behringer RX1602 Mixer, straight to the sound card of the computer. There is absolutely NO EQing of the Received or the TX Monitor Signals!
This is an explanation of what you are seeing & hearing...
The modified TS-950sdx is flat from 20cps to 5.5Kc within 3dB and you can see the "linear line" of what your speaking of when either Greg, or WZ5Q, has UN-keyed the rigs and there is nothing but White Noise from the band. What you are calling an EQ'ued signal is in fact EQing as you suggested, but it is FROM GREG's EQ!! Greg does not un key his rig on his speech pauses, and the receiver is picking up HIS room noise from HIS EQ Filter profile.
If an EQ was being used on the Receiver, you would see this effect on the White Noise of the band when the rigs were un-keyed, and it would NOT be a "linear line" as you call it.
This is a link to the audio clip,
We hope this clarifies any misunderstandings or misconceptions.