Yes, that is because of the real-world conditions that people experience between charging with an alternator versus charging off a constant and steady wall-voltage.
If you think about it, your alternator is anything but steady, unless you live way out in the country and once you pull out of your driveway you're doing highway speeds until you get to where you're going, and then you turn it off; whereas the electricity coming out of the wall is essentially extremely steady. Sure, if you got a map of the electrical provisioning area, you could easily find voltages at 122VAC right next to the tower or distro-plant, and way down at the end of the line it might be something like 111 VAC, but if you monitor the actual output from a single wall-socket, it's going to remain quite steady, maybe varying a volt or two, with maybe a 2-3 volt dip if/when your AC compressor kicks on or if someone plugs in a vacuum cleaner.
Because of the steady power output of your wall, it's much easier to build-in the proper power program in a wall-charger to be able to properly detect battery-voltage and step up the charger-voltage while also reducing the current so as to get a proper charge-curve (like I linked earlier) whereas most alternators are supposed to have a proper voltage-output, but their current ratings will be all over the place based on engine RPMs. Sure, you've got a nice output on the highway, but then all-of-a-sudden you've got to hit town during rush hour, and your alternator lacks the current output to get an effective charge, especially if it's got to step-up the voltage in order to charge a battery past around 90%. And that's primarily because a long, long time ago, some engineers made the decision that a battery at 90% is essentially just as good as a battery at 100%, and it side-steps the weird charge-curve voltage-detection needs as well as the fluid voltage step-up with the simultaneous decrease in current.
Basically the alternator is a hack and a patch to prevent a problem from happening. It assumes that you're starting with a mostly-charged battery, usually something at least 80% or so, that you might drain to around 75% starting the engine up in normal conditions. Perhaps you've left some lights on for awhile and/or had a really rough time trying to fire it up, oh well, it should work all the way down to around 60% or so, maybe 50%-55% if you're also using some starting-fluid. The alternator is capable of handling the charging-needs of a lead-acid battery from around 33%-50% up to around 90%, where the charge-curve comes back into play. This zone is known as the "bulk-charging" portion of the curve, and is pretty much set-and-forget throughout the zone, having a set voltage, and pretty much being able to handle almost as much current as you can throw at it. Which makes the alternator pretty much a perfect tool for that job. You don't really lose much (for the application) because the alternator cannot adequately finish the job, and the only downside is that after around 5 years or so, you'll have enough sulfation on the lead plates that your battery's maximum KWh will decrease to a point where it might become a problem. If you increase the size of the battery slightly, such as I did on my ranger (using a full-size pickup battery) then you wind up with a system where your battery will usually last 10 years or so before you need to worry about it not being able to handle the load it is designed to.
And, if for any reason during the life of an auto battery (as opposed to a house or deep-discharge battery), you happen to have a reason to hook it up to a wall-charger that can detect the need for and perform an "equalizing charge", which essentially has the ability to vary or "vibrate" the electrical charge as it's charging, then it is supposed to "knock the sulfates off the lead plates" and cause the sulfates to be reabsorbed into the acid, essentially making the battery as close-to-new as you possibly can get based on the specific-gravity of the acid contained in the cells. Doing this can extend the life of your (truck) batteries, and I've personally had el cheapo walmart batteries last for almost 20 years doing an equalizing charge every 2-3 years. A proper equalizing charge will usually take somewhere between 12-24 hours to complete, but most chargers will tell you to leave it for 24 just to be sure; that time-period is generally based on something like an RV or other unused battery that also needs a topping-charge in addition, and will usually have some kind of extra or red LED to indicate that it is in the middle of an equalizing-charge, and should not be unplugged.
C transformer likely won't help you much, but it also won't hurt, either. Essentially, it's just a 1:1 transformer which isolates each side from the other, so transients like when your AC compressor kicks on, or when the motor is starting, won't generally affect what is happening on the other side. If you were going to do anything, I would say that one of those heavy-duty 1-3 Megafarad mega-capacitors like they use for insane stereo systems placed in-line between your load and your batteries would solve any issues you might be having. Ideally, somewhere between the "Master" side of the bus-bar and the battery itself is perfect.
