Nosler most likely chose the more popular bullet weights for the 7mm. Seeing they are called long range no point in making a 150 or lighter bullet as the BC wouldn't really yield high BCs.
Perhaps they stopped with 175 gr and didn't make a 180 because some shooters might not get it to stabilize with a factory twisted rifle. (Remington 7mm rem mag barrels use a 1 in 9.25 twist)
Berger offers a 168 and 180. I have crunched the numbers of each with the velocities of a 7 STW a while ago and they have very similar wind drifts out to 600 yds or so. Sure the 180 has more energy but the 168 has a flatter trajectory.
IMO the 168 LRA might be a better choice with smaller cases like the 7-08 or 284 win and the 175 LRA would be the best choice with a 7mm Rem mag or larger.
I think it's just a marketing tactic. With out being able to see the bearing length ect. I'm going to assume that the 168 has a slightly shorter bearing length, as far as common shooters are concerned I doubt you'd know the difference. I am curios to see what physical differences there are between them though.
Keep in mind the animals we shoot for food and display are not bullet proof. Contrary to popular belief, they bleed and die just like they did a hundred years ago. Being competent with a given rifle is far more important than impressive ballistics and poor shootability. High velocity misses never put a steak in the freezer.