[csantini]

I think it's just interest rates.

I can easily get 3% per year investing in safe bonds, so I expect at least 3% to put money on any 100% safe bet.

I want to be paid for waiting X months

[chrchr]

That doesn't explain why there's a market for "Yes". For "No" to be worth 3% instead of 0%, there must be people who think "Yes" will in some way be worth 3% or more.