The real Arcade controller for that game, is a Dial / Spinner (Optical).
(It looks like a standard Pot driven wheel in the front... but its Optically read in the back of the assembly)
It is true that the Road Blasters yoke uses optical inputs like a spinner for steering, however this controller has a feature that spinners do not have -- bumpers that limit the rotation.
AFAIK this is the only game controller that has spinner/mouse-like optical (relative) inputs with physical (absolute) limits.
The game code and controller combine to provide a type of autocentering.
- If you turn the yoke all the way one way, then all the way the other, then return it to the spring-loaded center, the car's wheels should be straight ahead.
If mame changed it, to appease to the general masses.. Then Im surprised, as they have always been very strict about being accurate.
That said, there should be an "Arcade" mode, or the ability to select "Optical" or "Pot"
Because someone might want to used the actual hardware, or a replica remake of the original hardware.
You could argue that:
1. There is a specific, limited number of optical steps between the stops, just like there is a specific, limited number of steps between the stops of a 270 degree wheel after the analog voltage from the pot has been digitally sampled by an analog encoder.
2. The stops on the yoke make it behave more like a 270 wheel than a 360 wheel or spinner.
3. Defining the input as "AD Stick X Analog" instead of "Dial" allows users (and devs) to use MAME's analog auto-centering code with non-standard controls.
4. Many devs don't have specialized controllers like the RB yoke so it makes sense for them to make the game also work well with non-standard controls. It's hard to squash bugs if you can't get to the stage of gameplay where the bugs appear.
If MAME 0.222 or newer sees an optical control when you launch Road Blasters, it will map "mouse X" to "AD Stick X Analog" for steering.
This works fine with a trackball or spinner so it should be accurate with an original controller (or remake) once you set the sensitivity.
- As an added bonus, the game also works well with non-standard controls like an analog joystick.

Scott