it doesnt affect anything in the way to make a track sound properly but ther is something wrong in the first quote.

the dB scale is not linear, but logarithmic. If you consider the power of signal in W (PW), then you get the power in dB (PdB) like this :

PdB = 10*log(PW) , where log means decimal logarithm.

To be more simple, if you multiply a power by 2, the gain is 3dB. So if we consider the 2:1 ratio compressor, if the input is over the threshold and increases by 10 dB, then output will increase by 7 dB (and not 5dB !!!). Thats because the dB scale isnt linear that if you look at your comp's curve it doesnt look like a straight line.

That is also useful to consider this when going in parties, just thnik that if the sound level is 6dB above what youre used to hear, its 4 times louder ... Quite painful for the ears imo...