If I was only going to have 2 center fire rifles for all hunting in north America 223 and 308 wouldn't even be considered. Neither is the best round in its caliber.
This kind of question seems to come up a lot here, and for each one I probably pick different cartridges

but i am sure that i have never picked those two cartridges.
For the high end I would go with a 7mm mag or better, probably an 8mm rem mag because it truly could take any game at any range I could shoot. And you can always load it for lower velocity/lower grain weight.
For the low end I would go with a 6mm rem/ 243 or maybe one of the many wonderful offerings in 25 caliber 25-06 comes to mind. They are all enough for deer and you can load them for lower velocity/lower grain weight.
In many areas it is illegal to hunt deer with a 223, meaning one of your two guns is a dedicated varmint gun to some people, 308 is a great cartridge but I would be hesitant to take it on a elk hunt in Colorado not because i don't think I could kill an elk with it but because It would cost me a great deal of money to get an elk tag, drive or fly up there and find a place to hunt, I would want enough gun that I could take whatever shot I got and be confident of humanly putting the animal down.
223/308 CAN kill any animal in north America, but its not about having just enough to get the job done, it's about having enough to know YOU can and will get the job done.
Now on the subject of riffle and ammo makers offering to many cartridges, I believe that many of the new cartridges are pointless, offering no advantage over established cartridges that doesn't mean there is anything wrong with owning them.
We have many cars and trucks in this country, and once you get past the marketing hype on them you realize that an f150 is going to do about the same thing as a Chevy 1500, but hey some of us like the car like ride in a Chevy while some of us prefer the slightly stiffer suspension in a ford, some of us want a 22mpg v8 some prefer the 30mpg v6, America is about Freedom and diversity.
I will probably never own a .223 WSSM, nor am i likely to own a 220 swift, or a 416 rigby, but there is nothing wrong with someone wanting to own all three!