I had a similar experience to this with a Sony laptop I bought. The hard drive in that died after around 18 months and I went back to PC world and they quoted £270 to repair it. I challenged it under the sales of goods act as that states that the goods must be fit for purpose for a reasonable period of time (15 months is not reasonable).
It's worth noting that under the sales of goods act, the warranty is actually an addition to your legal rights and not instead of. Therefore, regardless of the length of warranty, you should insist they fix it free of charge.
You say you challenged it. What happened then? Someone posted here that they worked for PC World and they would try to get out of it. (On the other hand, I suppose if PC World fixes your Mac under the sales of goods act, then surely the manufacturer (Apple) would end up paying for it? So are they just trying to sell a very expensive repair where they make profit? )
All in all, it seems that the best advice is to buy Apple products at an Apple Store.