Because to anyone familiar with Spanish, Cervélo (particularly with the accent on the second e) rhymes with huelo. If they want it to rhyme with yellow, they should really remove that accent.
I speak Spanish as well. The accent is generally just that it shows you which syllable to stress. The pronunciation, just like in English, comes from the arrangement of the letters. Neither Spanish nor French underwent the vowel shift that English did though, so all the vowels are pronounced differently than they are in English.
I agree that your long 'e' is correct in its sound. I just wouldn't make it long because of an accent; I would stress it though. Either way, call the company and try it out: +1-416-425-9517. I am sure they will be thrilled to get so much activity on their voice menu
