But, under the ECPA, it is not a felony for system operators to do the same thing (for operational and diagnostic reasons) on networks carrying voice traffic. And yet nobody is suggesting that voice traffic isn't subject to wiretap laws.

Do you have a reasonable expectation of privacy for your bedroom or can the government freely search that too? Does your answer change after you hire a housekeeper (or housekeeping company) to dust your furniture and put away your socks?

You can't exclude the testimony of your housekeeper that your sock drawer was full of cocaine on the basis that you had an expectation of privacy, so yes, it changes a lot.