No, what he's saying is you shouldn't try to sell a TV with a full suite of modern hookups and another with nothing but those two little screws in the back on the same shelf, for the same price.
Even more, you should not restrict some of your stores to selling only the antiques.
Nobody is talking about doing that. We're saying that you might not be able to use your favorite toy in every game.
Spells are tools, a good spell caster knows which tool to use in which situation. Thats part of the fun.
Saying "i cant charm a zombie, thats not fair I love charm, i should be able to use it on everything. I'm going home" is just ridiculous.
Its like the little block game that babies have. Your trying to stick your square charm peg in the zombies round hole. Half the point of the wizard is that he's the guy capable of looking down and saying.....
"gee this is a square, i need a round one. Fireball..... .thats nice and round for the zombies".