I wish I'd found this thread earlier it's interesting. Hope all goes well OP.
I think the amount of time that is reasonable for a PS3 to last is very subjective. There were people that had played MW2 for 3 months plus online after it had been out about 10 or 12 months

. Should PS3s that spend a quarter of the year running last as long as those that get used for a few hours a month? That's where this become really strange for people posting on here. People that use their PS3 once a week or so will expect a long lifetime but those that hammer theirs for 3/4 hours plus a day will if being realistic expect less of a lifespan.
A PS3 is unlike a lot of other devices in that it can be the hub of entertainment for the whole household. Used for watching DVD's/Blu-rays, downloading and storing films/music, streaming music videos live as well as actually playing games and more. £300 is a lot of money but the PS3 does do an awful lot for that money and because of all that it does for some it gets used a lot more and therefore could have a lower lifespan. There are also quite a lot of moving parts in there and the more things that move the less reliable things tend to be as a rule. I would expect a stand alone blu-ray player that does one job to have a longer lifespan than a PS3 does for example and so if you were to say that a Blu-ray player should last the full 6 years you are allowed to try and claim under the SOGA then how long should a PS3 last?
Goods with moving parts will only last so long. If an exhaust wears after 3 years of use we are happy (well not happy but you know what I mean) to pay for a new one to be fitted but if our PS3 breaks down after 3 years we instantly assume that it must be a manufacturing fault and we should get everything for nothing. Why is that? A PS3 is a serviceable item just the same as a car and they are both covered by the SOGA.
Expecting a PS3 to last the full life cycle of the product (10 years) just because Sony have stated that the PS3 as a format should have a ten year shelf life seems a little extreme as well. CDs were launched in the late 80s and are still going strong, should we only ever buy one player?
All of the above still doesn't actually indicate that I am against claiming and hope the OP gets what they want. However I am saying that stating "something should last X amount of time because of Y" is not really the full story for me.