As a kid playing with Standard Gauge trains, the couplers become a significant part of the experience. It's the part you are most often messing with, making up or taking apart trains. You become very familiar with the coupler type used by "your" trains.
Later in life, if you came across what purported to be a reproduction on "your" trains but did not have the authentic coupler, you would consider it an imposter, not the real thing.
For me it was my dad's Ives couplers, and to a lesser extent the Lionel latch; that's what were on our trains and what we learned to manipulate with little fingers. Most of these Standard Gauge coupler types were called "automatic", but of course are not, they require hand intervention. If you lined the couplers up perfectly and backed up just right, occassionally you could get a train to add on a new car, coupling "automatically", but it worked rarely enough to be a thrill. The Ives coupler is the only one that will do this with any predictability.
Bing hook, Lionel crinkle hook, Lionel hook with ears, Lionel latch, Ives automatic, Flyer slide one-way and Dorfan lift-latch one-way. Most MESG (McCoy, CMT) use simple hook unless they are reproductions in which case they use the original. Part of the fun of rediscovering Standard Gauge as an adult has been to discover these different and ingenious ways the other companies made their distinctive couplers.
The differences are not insurmountable if you want to mix and match cars. Adapter couplers, adapter cars (with an Ives coupler on one end and a Lionel on the other, for example), changing out a coupler if it's a more or less permanent situation. A bread-bag wire twist-tie is the ultimate solution that always works, interfacing any coupler type with any other quickly, securely, and easily undone.
But it seems like a bigger issue than it actually is in practice. More than nine tenths of the time you'll run Flyer cars with a Flyer engine, etc. The different manufacturers' products are quite distinctive in many ways other than the couplers, and mixing them up in one train turns out not to be all that satisfying.
It's all part of the fun.