Co-ownership is pretty much a norm - even when pups are just exchanged between already established breeders. That way Ch fame goes both-ways and it is understandable.
Co-ownership is very clearly established relationship with little space for "wiggling" , while fostering can be allllll kinds of arrangements - whatever breeder and new owner decide to do. To be honest, I never saw "fostering" happening in major top lines in the USA.
I would find purchasing a show puppy much easier "long distance" than a pet - since I expect from a pet much more than just being "correct" in confirmation and with an OK temperament and also show contract is so much more clear regarding what is warranted and what not .It would be for me more like a business transaction and not a lot emotions involved.
Every top breeder has great interest invested in sending a really top quality puppy to a "show -home" !!! Somebody else will raise a dog and bring it to Championship and one more Ch is added to his/her line record !!!