They don't give a set amount of time, instead saying "reasonable lifespan". That makes for plenty of arguing over what reasonable is. My gran's cooker is well over 30 years old! Is it reasonable to expect that from ours? My old PC's motherboard died after ~2 years, is that reasonable? I'd say no in both cases. 30 years is amazing, and 2 is not enough.

Then you have to prove it failed due to a design fault, and the burden of proof is on the shopper. It's usually impossible to prove for the average person as the shop can insist that the proof isn't good enough.

Words like "reasonable usage" are also thrown in to further complicate matters. Playing on your console is reasonable and expected usage. Ah, but did you use it for more than two hours at a time? Sorry, that could be unreasonable if the shop wants it to be.

Most shops sell extended warranties. If you buy one then you get your legal rights without hassle. Otherwise ...

IIRC it was £50 for a warranty on my 360 which allowed me to take it back to the shop for immediate replacement if it broke.