salaries rarely and hardly ever go down. however inflation does exactly that in real terms. This is an interesting article about it: https://www.interfluidity.com/v2/9566.html
But the accounts 1 and 2 on VCE 4 (the ones funded by Monero) weren't registered in either Morgan's or Lichtenstein's name. They were created with fake credentials.
The feds were able to link them to the couple because bitcoins were moved from VCE 4 to other accounts that also had received bitcoins which were traceable to their alphabay accounts.
If they had funneled everything through monero I can't say that they wouldn't have got caught like this.
"Tu quoque" is a later tradition. According to Suetonius, who writes more than a century later but is our oldest source on this, the literal words were in greek and it was "kai su teknon?", which is literally translated as "You too son?".