I can appreciate your love of the extra class for all of the reasons you've mentioned. However, I'm not sure DXing would be a benefit to most of the people reading this article. The article is intended to get the average expenditioneer up and started. I'm not aware of any limitations to the general class for your second point, communication with countries outside of the US. For the pure sake of communication, isn't there enough overlap just in the general class or lower? Again, if the goal of the article is to get people started in DX competition it would be written entirely different. I'll admit, I really don't know much about the laws in other nations as it concerns amatuer frequencies. I'm not a dxer at all. Not yet anyway =).
Your article serves its purpose very well and for someone that is merely wanting the utility of the radio as an appliance for the vehicle during trips....you've covered it. For someone that may be interested in the hobby...intentionally or not, you've sold it a bit short and it reads as though the Extra class license brings little benefit. To an active amateur it brings huge benefits.
My point is simple, if you talk outside the states often enough, that extra chunk of the bands can make the difference between your ability to talk with an equivalent (secondary) license class from another country or not.
If you've ever spoke to anyone outside the contiguous states.....technically you're a DX'er. DX is not necessarily a competition thing, it simply refers to any QSO attempted or made outside ones own country. A General or higher class licensee can do this routinely.
Using 20m phone as a first example: This is globally accepted as being the most reliable daytime distance (DX) band. The General class runs from 14225 to 14350, but if you're familiar with the activity on the band you'll know that relatively little takes place above 14300 with most activity occurring between 14150 and 14300. Half of that bandspread (14150-14225) is in the Extra class, and there is more activity occurring in the Extra portion than in the upper portion of the entire combined band. A Kiwi operator that holds an equivalent "General" class license has phone privileges that span both our license classes. He can call for US stations in our Extra portion where only Extras can answer, and this recurs often. And so, as an General here, if he's calling on 14195, as much as you may want to talk with him...you can't because you have diminished privileges from what many other countries may enjoy.
Using 40m phone as an additional example: This is generally accepted as being the most reliable nighttime distance (DX) band. The General class runs from 7175 to 7300. But again, if you're familiar with activity on the band you'll know that as propagation changes in the evening the international broadcast stations (megawatters) will bomb the band with strong, broad carriers that leave little of the band left, except below 7200. That leaves a very narrow band for a General, unless he can find a spot to "shoehorn" himself into between carriers further up. The lower Extra portion seldom ever suffers this problem and is wide open most nights.
If any of these HF privileges were to benefit someone here, it would be for those who travel to really remote areas...areas beyond the reach of FM simplex or repeaters, and those who would actively use their radios to maintain a link.
I hope this illuminates the Extra privileges as well as your post did for the overall.