At one end of the scale it's no different. I've owned devices where they shipped with a CD containing some version of the firmware that had passed their internal QA and they never released any other version. That firmware might just as well be on a ROM welded to the board and I don't feel at all uncomfortable owning such hardware even though the FSF don't like it.
At the other end of the scale you've got systems where the "firmware" is very much a constantly developing independent software project whose source code you can't see and which is capable of operating somewhat independently of the CPU. Newer drivers (which get pushed into the Linus source tree) may require a newer firmware, leaving you with little choice but to update as the vendor desires. If you do something the hardware manufacturer doesn't like, a newer "firmware" can retaliate, you are not really in control of your own hardware after all.
The Raspberry Pi GPU firmware is definitely leaning over toward the second category, this is actively developed code, if somebody figures out how to, say, reverse engineer a RPi into doing something Broadcom wish it not to do you can expect to see updated firmware to resist that, albeit the foundation would probably try to spin that as a bug fix or something.