I can agree with that, sort of... If you're in black bear country, an appropriate firearm would likely be an excellent choice all by itself since it's far easier to stop/kill a black bear. I can also agree that in the lower 48 you're more likely to run into two legged trouble than four legged, and again the gun makes the best choice.
The problem is... 95% of the bad bear encounters you are going to have is when the animal is simply "too close". Are you going to shoot every one of those animals? Why not carry some spray to squirt them - and give them the object lesson that it's bad business to approach humans?
It's just my opinion, but I think your best choice is to carry both items no matter what kind of bears you are likely to encounter.
Several people have mentioned Counter-Assault as the spray of choice. Actually though, I think the product put out by UDAP (udap.com) is probably the best on the market. It has the strongest formulation and the longest range of any of pepper spray on the market. In addition, it makes a loud whistling sound when discharged and this sound seems to frighten bears even if the spray somehow misses.