There was a time foam was not widely used, prior to earbud quality not able to perform low and high end musicaly. Earbud were then sold for purpose of communication or low def music. Therefore foam wasn't that necessary. But today earbuds are capable for music, that's why foam is necessary too. Hence , manufacturer are tuning it more high frequency out of the box.IMO earbuds needs foams. I always wear foams on them, sometimes two on each side to warm the sound or improve the fit.
Seriously, how can you get decent bass without foams? Also, the upper mids and treble should be peaky and piercing as hell.
Unless a specific earbud is tuned to be used without foams, I just don't see the point.
Oh crap my imagination answer my own question.