Originally Posted by cityflyer369

Yes, people can buy two seats (they typically need a reason though, like being overweight, having a guitar with them or whatever). With AF/KL both seats have to be in the same booking class. (You get miles only once though.)

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What we should not forget when discussing Business class in Europe is that, due to minimum stay conditions and the high prices of one-way flights in Europe, business travellers often have to buy tickets in the highest fare buckets. The price difference between these high fare buckets in Economy and Business class fares is typically quite small, so that the better food and the blocked middle seat (and the extra miles) are often worth the money.
Additionally, some companies have travel rules according to which you can fly Business if doing so is no more expensive than 10% above Economy, for example. For 1 or 2-day business trips on short-notice this is often the case, so people fly Business.