More than a few new gun buyers read just enough gun / hunting magazines to get a distorted view. Not many magazines "on the stand" today have articles that promote the 308 or the 30-06. Many articles do promote newer rounds that are "better" than the "traditional" rounds that include the 30-06.
Hype does sell. Its all about the marketing. You know, "May the schwartz be with you".
Now lets look at reality.
To start with, consider that at least 95% of the people who are choosing a caliber while at a gun store do not and will never reload. As, such over the counter ammo is what really makes a difference between all of the otherwise good choices. Tell them to think both now and 20 years from now (resale value and/or to be handed down to a kid). Think of how many guns are out there chambered for something that has become nearly unobtainable.
For most rifle buyers in the category being discussed, hunting capabilities of the 30-06 and the 308 with factory ammo are essentially the same as far as the target is concerned. Some 30-06 guns will be slightly heavier. Recoil of both is near the max that an "average Joe" will consider acceptable. Both "just work".
Both of these rounds have a huge ammo selection / availability / cost advantage over other bolt guns.
Ammo supply and cost is almost as good for the 243 and 270. The 7-08 is marginal for optimal ammo availability. All three of these rounds have some real advantages for some hunters.
Some of the newer rounds may have adequate availability now, but will they in 20 years?
If a guy comes into a store looking at bolt guns and is willing to listen to the salesman, then my first suggestion would be to discuss ammo availability. Promote guns that will be easy to find ammo for at the only ammo supply store in a 60 miles radius while they are hunting in some remote location in ten years. Tell them to think of all of "hot" guns of 10 - 20 years ago that would now be nearly useless to them due to ammo supply.
Of the rounds I have mentioned, most will get the job done just fine. For general purpose hunting in the US, the 7-08 is probably the "best choice" by function and the "worst choice" by ammo availability. The 243 is really only something I would recommend where lower recoil is a priority. For someone anticipating longer ranges, the 270 is a great choice. And for anyone not wanting one of the above, they would do well to pick either the 308 or the 30-06 purely based on what ever sounds best to them.
Lots of other rounds actually have real hunting advantages in the US over the 308 / 30-06. However, these advantages (less recoil, flatter shooting, lower gun weight, less muzzle blast) are "nice things" that do not really translate into "higher percentages" for getting the job done. However, except for a few (243, 270, 7-08, 30-30), these advantages come at the cost of reduced ammo availability and significantly less assurance of future reasonable ammo availability.