Most of the assumptions and reasonings in the question are spot on.
However, one is not:
These are older versions of the firmware, and you can't use them to update your firmware as you'll obviously have a later update, neither to downgrade the firmware either.
This is not obvious and not necessarily true.
First of all, these updates are for Intel-based Mac-computers. Those came out in 2006 (MacBookPro 1,1) and had a modified version of Mac OS X 10.4 Tiger installed. Some of those may still be around and were perhaps never updated (Grampa likes his tools to not change).
While you and Apple seem to assume that
Most firmware updates are automatically installed when you update or upgrade OS X. Some firmware updates are also available as downloads you can install manually. If your Mac needs a firmware update and it isn't installed automatically, check to see if a manual updater is listed below.
This "most" is invalidated in companies or schools that rolled out installations as images, not via an actual installer. With this now no longer recommended method you get a fully functional OS installation, but as the install-part is skipped, so is the installation of firmware updates. This is true even for the latest versions of macOS, which in theory require updates delivered within the installer for APFS compatibility, but if you bypass the install (for example to keep your filesystem as HFSplus) and go the image route you also do not really need these parts of updates. This method was recommended by Apple in the good old days…
Some of those models listed oin that page are also of vintage status and not supported by the newest versions of macOS which rolls out firmware updates by OS-installation. All those models not supported in Sierra…
Or as commentator Allan put it:
If you’re running an older version of macOS/OS X for application compatibility reasons and cannot upgrade to a newer version. That’s one scenario…
So there were many and there are now a few cases where Macs were in operation with an older firmware version despite updates being available. Since these updates usually contained fixes for serious problems discovered and then tried to be rectified via such an update, it is usually a good idea to ensure that they are kept at their latest versions.
One usage example: You get your hands on a "sold as defect" MacBook Pro 15inch early 2011 2.0GHz with Mac OS X 10.6 still on it cheaply. You can be sure that the firmware is outdated. The GPU chip is now broken as so many, the battery out of juice. You replace the battery and revive that thing with lobotomy of the GPU. You then boot up and install a younger OS, Yosemite performs best on these. You turn on full disk encryption FileVault2 and notice quite a slow down, also your brand new battery behaves suboptimally and soon says that it will need replacement.
How to fix that?
You improve energy management with an SMC update that improves the loading behaviour relating to the battery.
Now that you enjoy a good energy behaviour you still notice the slowdown from FileVault2. Why is that? The CPU in that model shipped as
Core i7-2635QM – AES-NI – No
meaning that the encryption has no hardware acceleration unlike the bigger models. How to fix that? Download and install teh EFI firmware update standalone installer for that model that for the last 3 or 4 versions contained very silently also a microcode update from Intel delivered by Apple in that way that simply enabled AES-NI on these lowly chips.