Breeders do this to save money most of the time, but your cat may not be properly socialized because it did not spend the additional time necessary with it's mother and siblings to learn how to play nice, use the litter box, etc. I see that this is the case much of the time these days, but aside from the obvious, it is good to have a kitten who has completed all of his de-worming and vaccinations before he goes to a new home.
Even our boy came to us younger than he should have, but we know better now. I noticed that is must have been Dexter (and aging a bit) that taught Bauer when not to bite and all of that because we were having an issue with him playing rough with us before we brought home our other boy. Thankfully all of that is resolved but every now and then it becomes ingrained and you end up with an unfriendly kitty.
A reputable breeder will provide you with a legally binding sales contract/agreement; which protects the buyer, seller, and kitten, and provides a health guarantee on the kitten, registration papers (provided the kitten is neutered upon adoption or after proof of neutering is sent to the breeder), pedigree (normally a 5 generation pedigree), a current health certificate listing any vaccinations, worming, or medications that have been given to the kitten being sold, a receipt of your purchase, and often a kitten package which includes a sample of food/litter/toys currently being used with the kitten.
I hope you made sure to bring home with you, all of these things. We got lucky in that our breeder provided us with everything except apparently the kittens best interest in that we got him early.
It's all too easy to be naive and trust that these people know what they are doing simply because they call themselves "breeders." Every once in a while, however, you run into one who isn't an ethical one, and instead is just someone who wants to make some quick cash off of exotic kitties they know people will buy on the cheap end.
Congrats on your new baby.