Example 1: Fred is a senior employee of a charity dedicated to promoting environmental awareness. His senior position gives him a salary which puts him in the higher tax bracket. The nature of his job involves a good deal of travelling, so the charity provide him with a company car. However, because of the charity's stance on CO2 emissions, they won't provide him with a 'gas-guzzler'. He's told that he'll have to drive a more environmentally friendly car and he opts for a Fiesta.
Example 2: Mary is a fairly well-paid freelance IT consultant. She runs her business as a limited company although she's the only employee. Mary has always wanted to own (or, at least, lease) a Ferrari. She considers paying herself, as managing director, a high salary (which will take her into the higher tax bracket) and then using part of her income to buy (or lease) a Ferrari. She realises, however, that it would be better to pay herself a lower salary (below the threshold of the higher band) and run the Ferrari as a company car.
Both scenarios are 'unlikely' but not 'impossible'. The people who compile the tables are simply allowing for all possibilities.
Chris