No matter your intended audience, there is always somebody who will need a dictionary. It's not shameful to look up words, and it's easier than ever to do so. You've shifted to arguing about conversion rates for non-English speakers, which is a fair, but separate point. (I'm also curious if small words and simple sentences really do translate to higher conversion rates.) I am talking about prose in general.
> PS Morose is not "very sad" :-)
Nor is awestruck "very amazed." The smaller your vocabulary is, the less you can communicate (as redblacktree pointed out, this is demonstrated quite dramatically by George Orwell's 1984, wherein the language is dumbed down so much and has so many words removed that the citizenry can't express emotions the state deems negative.)
This is the truly tragic thing about this incessant anti-intellectualism: people lose some measure of ability to express what they really mean or feel, all in the name of meeting the lowest common denominator.
(For the record, I am not a native speaker, and I love seeing words that I don't understand.)