Advertising is a skill which must be learned. The trick is to make sure that you make statements which sound good but commit you to nothing; for this purpose, dodgy mathematics frequently comes in handy.
Take an advert I saw in the paper, for a TV: "This TV has a lifetime of up to 100,000 hours". Now, at first glance this sounds quite impressive - your new TV will last up to 4166 days, or 11.4 years (which brings us to some secondary dodgy maths - because 100,000 hours sounds quite impressive, but 11 years, for a TV, isn't all that great. Mine is about 15 and going strong. But I digress). The problem arises with the second glance, when you realise that 'up to 100,000 hours' technically means 'less than or equal to 100,000 hours', which is anything from 0 hours to 100,000 hours. So, really, it could break next week, which isn't so hot.
In fact, the only way the advertisers could be hauled over the coals for making misleading statements is if the TV lasts 100,001 hours, so I'd say it'd be a fairly safe bet that they've made it so it won't.
I find that much the same thing happens with energy-saving lightbulbs. Now, I don't want to discourage anyone from buying these, but I do want to point out that when they say 'lasts up to 10 times as long as a normal bulb', they're not proved wrong if it blows up the first time it's switched on - this is simply an instance of it lasting 0 times as long as a normal bulb, and since 0 is less than 10, they were correct.
This is probably all the fault of the EU, or the Office For The Prevention Of Misleading Promotion, or some such, or else advertisers have just realised they're onto a winner, but of course the phenomenon has spread to everyday talk, and this is how we get Liberal Democrat leader Nick Clegg claiming he has slept with 'not more than 30 women'.
Which sounds (and was heralded by the media as) rather on the enthusiastic side, until you realise that I could make the same claim myself, and not be lying.