It's a bit more complicated than that -- RIs are bonds with unknown future payouts (since the hourly prices drop from time to time) and a very high transaction cost (AWS takes a 12% cut each time an RI is sold).
Further parallels with options are: 1) your upfront payment is option premium; 2) your RI has time value which is always declining as time passes; 3) RI gives you a right, not obligation, to do something; 4) RIs have many series, each expiring at the same time, just like exchange-traded options that expire at predetermined times.
All in all, this is huge. Or even bigger than huge. It can enable certain things that were not possible before, and personally I am very excited about opportunities it will present and how it will re-shape public IaaS.