Not really... keep in mind I'm speaking on my own behalf and not as an employee.... I can only recall two or three people ever asking us about burning a .IMG file. And for those that want to and only have RecordNow I just ask them to rename the file to .ISO and all works well.
In CloneDVD I know you can choose to show ALL files but there is not a specific setting for .IMG but again it works fine. If you want it to show up in there without choosing to show all file types you can just rename it to .ISO as well.
I can promise you that it was not an intentional "we don't want to burn .IMG files" decision... but it is a less common file extension.