In reply to woolsack: bear in mind that, in both cases, something in the region of £6 is spent on bottling, labelling, transport, vat, duty, marketing, and the various negociant, importer and supermarket profit margins. So one contains about £2 of wine and the other about £6. Yes, the difference is very easy to tell - to me at least!
I suspect that there's some inverse snobbery at work here. Also, as a rule, better wine needs longer in bottle to become mature. If you buy good claret (which often has particularly long maturation times, especially in top vintages - mid-range 2000s are just about ready now) and drink it immediately you will indeed conclude it's rubbish, because it'll be over-tannic and raw. Give it a few years and it'll become lovely.
Grumpy, with respect, the point about the Wine Society is that they don't do discounts. They almost never have sales, they just sell wine to their members for what it's worth. I've disliked the odd bottle from then but never ever thought it was anything but fair value. And that's enormously reassuring.