Basically, it's an easy way to add another 30% to a number on a chart. The intent behind doing so could vary from simple negligence, to outright misinformation, and like many things, the truth likely resides somewhere in-between.
Personally, hybrid electric vehicles seem to be the most viable current option for almost everyone, and it gives us some time to get the power grids upgraded enough to move to all electric later. That in my eyes is an ideal situation, as it gives battery tech, and generation tech, time to mature further. Sure 300-some miles in a nice Tesla is an achievement, but, 1000 miles, half the weight, twice the generation efficiency, and half the charge time is better overall, and from what I'm seeing, all of the above is doable within 10 years or so.
The Prius Prime is approximately the same weight as the Model 3, more expensive than the Model 3 after the rebate, and only gets 2.9 miles/kWh vs 4.1 miles/kWh for the Model 3. So it takes at least 33% longer to charge for the same distance of travel while slow charging and of course doesn't support fast charging.