No, they absolutely can. You may be confusing this with various first amendment cases about compelled speech, given the focus on a court ordering code authorship. A regulator does not have to concern themselves with the mechanism of storage, they can simply designate communications as requiring storage. And they have done so in the case of electronic transmissions. The relevant law allows regulators to compel retention of written communications. Storing a communication in memory and sending it over the network to the memory of another computer for display is by itself sufficient to qualify as a written communication.