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.
but in IEO investors are given security, I think if the exchange opens IEO for fraudulent projects, the good name of the exchange will be bad. and they will be able to lose a lot of trust, I personally still see method in IEO because at this time IEO is just young, still have to see the potential for much longer