Until recently, it's really the only way to acquire pet newts. I'm a casual hobbyist and have a strange urge to buy a newt every time I see a beautiful specimen of a type I've never owned before, though this has only happened on a few occasions. They were years ago, and long before I really knew much about the pet trade.
I have a Cynops pyrroghaster that I'd received as a Christmas gift when I was 11, and that was before I even began to suspect that pet stores knew nothing about newts, but she's still alive and well.
I once bought a beautiful Tylototriton shanjig at a pet store on the spot about 10 years ago (I still have this one and he appears to be doing fine) simply because of the thrill factor of never having seen one of those guys up close. He (or she--I'm still not certain) was in a semi-aquatic setup, which I quickly learned was inappropriate for that species, and I was told it was the first day it arrived.
The second time it occurred was when I purchased my Pachytriton from a pet store about 7 years ago. At the time, I didn't know anything about this genus and thought it was some sort of mislabeled plethodontid salamander. The slimy skin and shape of the body are what threw me off, as well as the fact that the label said this was a "Taricha" newt, which I knew was incorrect.
I love my newts and I'm glad they're all doing fine, at least as far as I can tell. Come to think of it, I've owned newts for most my life. The first one I think I had since I was 5, and since then there have only been two brief periods, each lasting no more than five or six months, during which there have been no newts in the household. The newts I owned before the age of 11 didn't last too long, and that was before I knew that handling newts was scarcely more appropriate than handling fish.
Now I feel sort of guilty about the newts I do own, since I've only recently learned about the decline of amphibians in the wild, and that they are almost certainly wild-caught specimens. It's inspired me to want to search for a place where I can 'lend' (or donate) my newts to professional breeders, to undo the possible damage I've done by purchasing them.