I think this could happen if sony wanted it to happen. Possibly at the detriment to ps4 though, so maybe its unlikely.
Unlike ps2 though the ps3 will recieve strong support in 2014 (Metal Gear Ground Zero/ Destiny/ Dark souls 2/ GT6/ more titles I'm sure will be announced and obviously the potential for LAst Guardian/FFvXIII to be released as cross gen) Add in a pricecut and we're looking at a fairly strong 2014, even with the ps4 out. People shouldn't forget about the "other regions" which still count for a fair amount of sales and will thrive when the ps3 is considered dead in the west.
I see the system reaching 80m by the end of this year and probably selling 6m in 2014 with a price cut. The lack of Backwards compatibility in ps4 will really help its legs I think. It would be genius for Sony to release a ps3 late 2014 with complete backwards compatibility with ps2 titles. at $129 I would buy one just to archive all my ps2 games which I have lying around.
2013- 80
2014- 86
2015 -90m
Eventual LIfetime sales 95m.
PS3 will not be discontinued till 2020 me thinks.