Now with more radium

@Antonyourknee  
I think the difference might be quantity. Applebloom, who is an aspiring Alchemist, goes through a shitton of trouble to get one drop of the potion that she needs. Zecora seems to be able to cure small groups, but her magic is limited to one effect per potion, and she has to forage extensively for specific ingredients. So a cure-all tonic sold in great quantity that only costs four bits is just credible enough to be true in a world with magic, and isn’t redundant because magic has limitations.
 
Also, I doubt there are an abundance of unicorns that focus on potion making specifically. It seems to be more in the Earthpony/Zebra talent range, seeing as they’re stewards of the natural world and adept at producing consumables. Twilight obviously has the knowledge but we never see her, or any other unicorn, use it a lot.

@RIG
 
@PonyPon  
Perhaps the idea of the tonic was a cheap,easy way to “cure”a variety of aches,ills and pains that standard medicine and mainstream healing magic have trouble with.Mabey getting a magic treatment is expensive since you need a unicorn that specializes in medicine to cure multiple ills and who would waste their hard bits on healing Magic(presumably their equivalent of surgery)on aches or minor ills(remember all those customers either had already treated their wounds and were just waiting to heal or had minor blights that shouldn’t require a doctor,much less a healing magic).Sure Zecora might sells some poultice or herbs to the sick pony but perhaps some lingering traces of mistrust of the strange Zebra brew might deter some of the more suspicious of the populace.

NUMBER ONE IN THE WORLD  

Pinkie: you could use a healing spell!  
Twilight: ….healing….spell? *then she realizes that not unicorn ever has thought that*

@PonyPon  
*as odd

@RIG  
Yeah, that struck me a odd, two.
 
Either those haven’t been invented yet, or unicorn magic just doesn’t cover that.

hell, attack magic is confirmed (magic beam!), but not healing.

@soundtea  
actually, yes, i expect that…  
but now i think about it, i have never see an unicorn do a healing spell…age, transformation, dark, shield spells all the day, but not a single healing spell….

@RIG  
It’s like you expect there to be healing potions sold at the dollar store.

@RIG  
Zecora will help her friends and those in dire need, but she’s no dealer.

this makes me think…Equestria is a magical land, then why there shouldn’t be magic elixirs somewhere?