They have though, pretty frequently actually. Everytime the Hub Discs get an update there's a change log, only sometimes when the actual hub gets updates they will tell us, like here:
(1 of the many examples) maybe @DanielS can help.
On my Hub it changed all the Line Atten and Sig Atten to higher numbers... Upload got really slower
FYI - you are not the only customer to experience slower speeds and higher line attenuation after firmware upgrade to SG4B1000E020 in the last few weeks - see these two posts:
It could be a coincidence, but perhaps there is a connection?