Maybe the deer nowadays are a lot tougher than they used to be, but for years the 30-30 was king. Shots inside of 200yards used to be as good as dead, out to 350 you had to know the range pretty well because of the trajectory. Magnums mostly just make it easier to hit at long range (flatter trajectory). Oh yeah, and they help sell guns, too.
Of course, now that the deer are bulletproof, only a (insert favorite number here) super magnum will kill them. Only problem is nobody told the deer they're not supposed to die when you poke 'em with a 30-30. Or a 44-40, or whatever. I still shoot my 7X57 and love it. And I don't miss very many meals, either.
I remember reading once to make sure your rifle had 600 ft-lbs at whatever range you were shooting to ensure clean, one shot kills. Pretty soon it became 1000 ft-lbs. Pretty soon it was absolutely required to have at least 1000 ft-lbs at whatever range or you wouldn't kill the deer at all! I wonder how those guys ate back when 45 caliber muzzleloaders shot a 180 gr roundball at 600 ft/second? If you do the math, the animals were safe (280 ft-lbs at the muzzle). Also, if you check, you only need 28 ft-lbs to pierce hide, 80 ft-lbs to break bone, so theoretically you could kill deer with a 22 LR, which a lot of poachers did (and likely still do). Lucky nobody told the deer.
Hunt with whatever you enjoy hunting with! Do it safely and aim well. Enjoy your meal.