First you are missing the fact the nobody mines with CPUs. Only GPUs are used, specially if they are from ATI because Nvidia sucks at mining. Then you are overlooking the fact that mining is not profitable for most people because of the electricity costs.
Amazon must have the datacenters at locations with cheap electricity so they could make some profits if they have ATI GPUs to rent. I am just not sure if this is something they want. You will have to talk to them, not us. With the decreasing price of bitcons and the time/money needed to coordinate the switch from mining to rental mode, they probably don't want to go through all the trouble of setting this up and then find out that there is nobody out there to buy their coins.
PS: Bitcoin is not a safe investment (we might not be here in a year because Bitcoin could be outlawed, prices could drop tremendously, etc). Big companies tend to avoid high risk investments like this.