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.
This is absolute a good explanation, if we are to be sincere with ourselves. So many people actual thought that IEO is the saviour, meanwhile it isn't. The early investors of IEO are the ones that get the bulk, aside the project team. Particularly, for IEOs that grow after listing.
A time might come that IEO will end the same way ICO ended.
IEO can end if they lose investors, as long as they have investors, the IEO will still be there even though the method used only has a difference in security between IEO and ICO but the current advantage is held by IEO. hope they don't disappoint for the future because investors have suffered a lot from fraud