Onan: As topic starter, I hereby give my gracious permission for topic hijack.
With cars, I have noticed this too and reckon it is a 'cheat' to allow easier access when getting in to the driving seat. Perhpas this started in the US where people are (ahem) a trifle larger than in the UK. "More trifle, Vicar?" Of course, no one is accusing Texas residents of being over-sized!
JF, many thanks for that run down of factors. Very helpful.