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.
Definitely there is little bit difference, If you agree or not. ICO is the uncertainty for the investors because they dont know how long time to wait for the exchange. They may have a long wait to be frustrated. I dont know which ICO is successful in last few months. All of the IEO's are big successful not likes that, a lot of fraudulent ico project will launch with shitty exchanges because exchange fee is cheap.
so in short ieo is less riskier because you will know if what ieos are good and bad if you will only based on the exchange listed by them but ico is purelly unpredictable but like they always said , high risk always leads to high rewards , there is a big potential on ico's compare to ieo's . take a look on the past , many ico's became succesful and give a good profit but look at ieos now , i havent seen lots ieos pump too much . if there are legit ieo's ,the gain are only minimal .