Publishing houses also do print on demand, as it is cheaper for smaller runs and there is less upfront investment. eg. the first 5000 copies come from a POD sup

Publishing houses also do print on demand, as it is cheaper for smaller runs and there is less upfront investment. eg. the first 5000 copies come from a POD supplier, and if things go well they do the sums and consider doing a run of 10-20k with a traditional print setup. On your bookshelf, chances are the 'trade paperback' sized books from the last several years came out of a POD printer (a glorified laser printer, often but not always with integrated cover and binding), and the smaller paperbacks from a traditional press. The POD books still get ordered in batches though, because it is cheaper to order 5000 copies instead of ordering a single copy 5000 times. Or lease a device from Xerox. Single copy POD is really only done through Create Space and their competitors, where customers order them directly from the printer.