I interpreted the question to be along the lines of how much you would need to be paid to quit work and never be allowed to work again, rather than just an amount to quit your current job and not feel the need to work again in a similar job. If it were that question I could understand reluctance to accept "only" £1m or £2m, as should there be some years of poor investment returns/losses you wouldn't have the option of doing some paid work to make it up.
I think in general though it just shows how clueless most people are about bigger picture financial planning and spending. As mentioned, the responses may have been more reasoned had it been explained in terms of income/cash flow rather than net amount. I suspect many people, due to not trusting themselves/being able to plan, would prefer to have 4% of £2m as income for life rather than £2m in cash. Firstly because they could immediately see how it would replace their salary (or how much of it, if high earner) and secondly because of the guarantee. Though of course really it would (given average investment returns) make sense to take the cash, as it would provide the capital and the same level of income.