PS3 came out in 2006. 2013 would mean the PS3 had 7 years on the market before its predecessor arrived. That's a long time for one generation.
Sony preaches the 10 year plan, well dont forget how long they sold PS2 after the PS3 came out.
Plus they already mentioned they raised R&D cost for the PS4. They are only giving lip service about PS4 not coming out for a long time because 1) They dont see Nintendo's Wii-U as direct competition and 2) They still want people to buy the PS3.