That is a good question Ryan. You'd think that these units would be coded in such a way that load times would be as fast as possible out of the box. My personal opinion is that load times bumps up against hardware more then firmware. CPU-processor speed, memory speed, read speed, etc. while not "fixed" its pretty dang close to being set by the capabilities of that hardware. Poor coding could of course make a CPU be weighed down by crap it doesn't need to do making the player seem slow, etc. But in general I'd say speed of the unit is hardware/firmware, not firmware/hardware.
In other words firmware updates/tweaks can only go so far in improving things like load times. Once that code has been optimized, there simply can't be much room to improve load times via firmware.
E.B. White said, "I arise in the morning torn between a desire to improve the world and a desire to enjoy the world. This makes it hard to plan the day."