
I think you have put your finger on it the decent breeders your seeing with older pups are not prepared to let their pups go to just anyone and will wait until the right sort of home becomes available, the current economic climate makes this more of a challenge.
The puppy producer has sales and will happily sell to just anyone who will buy, and some will dump unsold pups on rescue. The worst kind probably do dispose of unsold older pups. There were a number of younger Viszla's found dead within the year 'Yogi' won at Crufts.
>e Who buys 4 - 6 month old puppy rather than an 8 week old though?
If it's a breeder worthy of the name, and they have brought the pup up properly as part of their family, with appropriate socialisation and training for it's age, then in fact I'd buy an older puppy any day over an 8 week old.
At 4 - 6 months it will have been mostly house-trained, is able to go out for walks (albeit not too long ones).
I think breed makes a huge difference, as with my breed they will happily bond with anyone during puppy-hood.
Until recently those of us who imported had no choice other than to have a pup at close to a year of age, and even now they can't legally come into the country until 16 weeks.
I have fortunately never had an unsold pup past the age of 11 weeks, though certainly have kept pups until around 16 weeks due to holidays, export requirements etc.
As the others have said you keep the puppy fro as long as it takes to find the right home. Fortunately in my breed there are plenty of people who would prefer an older pup or young adult.