Backwards compatibility is a big factor in a console's success. PlayStation 2 could play all PlayStation games, and PlayStation 3 had options for both past consoles at some point or another. We've just learned that because of the setup of the PlayStation 4's innards, Sony has opted not to allow the console to play games from their brand's older consoles.
As an alternative to loading older discs, Sony has decided to offer a cloud-based game streaming service that allows PlayStation 4 owners to stream games from older console generations to their new system and play online. While this is a great option for players to have, making it the only available option cuts off dozens of users whose internet is either too unstable or too slow to support this kind of streaming. Hopefully in the coming months, they reveal an alternative way to play older games, such as the PlayStation Classics section of PSN. Until then, cloud-based game streaming is the only service we can be sure of.