For one thing, before we can distinguish between the two sample responses you give we need a defined point in time at which the IOU issuer is obliged to give a response at all (a settlement date).
IOUs (taken as meaning any acknowledgement of debt) don't necessarily EVER have to be redeemed. For example perpetual bonds are never intended to be redeemed - yet are debt.
Thanks for your valuable arguments. You might be right and I think I understand now why theymos said IOU is not a binding contract. But now I feel totally confused. What is debt then, if it is doesn't ever have to be repaid?
Debt is something that you owe - a claim someone else has against you. Not all debts are created with the intention of being repaid (e.g. loans that are made for tax reasons without either party to the loan having an intention of there ever being a repayment). Perpetual bonds are another example of debt that will never be repaid (talking RL ones not the pretend mining ones on here). The bond issuer borrows money that will never be repaid - paying interest (a dividend) on it regularly. The only way to get your cash back is to sell it to someone else.
That's why debt/IOUs with no agreed terms is worthless.
Maybe an example will help - for the examples below the assumption to be made is that I WILL honour any commitments I made (in practice all debt should be discounted in value based on your confidence that I'd repay):
If I said I'd owe you 20 BTCs to be settled in a week in return for 10 BTCs from you now then (IF you had total trust in me) you could reasonably value those 20 ripple BTCs at similar value to 20 actual BTCs.
If I said I'd owe you 20 BTCs to be settled in 5 years in return for 10 BTCs from you now then (IF you had total trust in me) you would STILL have to value them at a lot less than 20 actual BTCs (as they'd generate no revenue in the meantime and were illiquid).
In ripple BTCs of each of the above scenarios are treated as being interchangeable (whether its 2 sets from same issuer or from 2 different issuers) - despite the fact they have very different actual value.
Now consider a third scenario (equivalent to perpetual bonds):
I say that if you give me 10 BTC now I'll owe you 10 BTC on ripple. I will never repay those BTC but on the first of each month I'll send 0.01 BTC for each BTC owed to whoever currently holds them. Again - to ripple those are just BTC - and swappable with anyone else's BTC (provided someone trusts both me and the other issuer). These BTC may have more or less value than the other ones - depending on how people value 1% interest/month against liquidity. But I'll never repay them - and am NOT a scammer for issuing them.
Now the final case. I say if you give me 10 BTC now I'll owe you 20 BTC on ripple but will only ever repay them if I win the lottery. What are those BTC worth? Nearly nothing (even ignoring the fact that I don't play the lottery).
Do you see how the value of a debt/IOU is defined by the TERMS that apply to it - not by its face value? But ripple treats them all based on face value.
TF's ones were pretty much explicitly worthless. In the absence of terms the only way to reasonably assess value of something is to look at what consideration was given in return for them - and assume a similar value. Nothing was given - so their value is gong to be around zero.
