The main reasons for people believing the playstation 4 release date is so far away are:

1. The PlayStation 3 hasn’t been on the market for long enough to bring in a new console.
2. The technology isn’t advanced enough to bring through an entirely new console.
3. The cost of engineering a console that is significantly different may be impractical.

But according to Sony there is significant room for overlap for the PlayStation 3 and PlayStation 4 to be on the market at the same time. The PlayStation 3 will be significantly reduced in price, whilst the PlayStation 4 will be significantly higher. Although costs will be astronomical to manufacture and ship two types of console, Sony has to be seen as keeping up with technology in order to be a leader in this fast and pacey market.