Of course, there's the rule in English that you cannot place two vowel sounds together, which is why we add that additional sound in between.
Like many things in our loose trollop of a language, there ARE exceptions, usually proper names/imports from other languages (aeolian, hawaiian) or scientific/technical terminology (molengraaffite, oogenesis, neencephalic). But then you get words like “individual” and “individuum“.
And of course, regional variations...
[video=youtube;Dd7FixvoKBw]https://www.youtube.com/watch?v=Dd7FixvoKBw&sns=em[/video]