First of all, for most of them, it's black magic. For the few who know a bit more, will be convinced by arguments of analogy (after all, nowadays many hard drives are in fact flash devices, and the details of interface protocol are beyond what jurors will care about).
That's what they're asking for. Part of the FBI's argument is that they need the information for safety of our country, not specifically for the trial.
However... in that case the FBI will have remote access to the phone in question to run whatever software tools against it they require. (This requirement is in the order. :) )
Given that "prevent iOS from reading the ROM used to boot the iDevice" probably isn't a threat that Apple considered to be a serious one, it's entirely possible that the FBI (or an agent of another TLA embedded within the FBI) could use this remote access to also gain access to Apple's (signed!) PIN entry delay and self-destruct removal modifications.
If this happens, and there's a way to bypass whatever mechanism Apple used in the modified image to make it run only on that single iPhone, then Apple has just unwittingly (and unwillingly) handed a backdoor to any iPhone of that model to FedGov (along with any other governments that have clandestine access to the systems of the TLAs in question).
Don't be confused; the stakes are really high.
The owner is dead, so the phone data is not needed for a trial against the owner.
It might be evidence against "co-conspirators" - sadly, we have a vindictive, lawless government now that likes to go after former roommates and acquaintances.
Also, you hire an expert to testify as to the technical details. It isn't perfect, but it is what it is; and anyway, the first thing a defense attorney will say/do in the case that the FBI prefers is to cast doubt upon the integrity of anything the FBI finds after all of the screwing around with it that's been done.
There's nothing interesting there.