the only difference is the middle letter. ICOs are scamming people by calling themselves initial "coin" offering and IEOs are scamming people by doing the same exact thing while calling themselves initial "exchange" offering.
the end result is exactly the same with different speeds at which they dump and exit. as IEOs are already supported by and listed on an exchange they can dump and run away faster.
Yes IEOs are just using the exchange to attract people in their project because everyone think that when the coin is already on exchange the project already succeed.
They just upgrade their strategies to scam more people because they know ICO already lose the trust of investors.