In general, the non english speakers are more interesting that the traditional premed, and I'll tell you why.
They have experiences that radically distinguish them from the american students. Most of them, not all, had to go through very difficult moments in their lives to achieve their goals. They generally have many outside of classroom experieces, from their countries of origin and from the their immigration experiences.
Relating ESL and MCAT: for ESL people it depends a lot when one has started to learn English. If you started at 6-7, it is different than if you started at 19 or if you started at 26. So don't try to compare all ESL people with one another, comparison does not hold.
I'll tell you one very simple reason why ESL score lower than the Americans on the Verbal portion. It is mainly because of the vocabulary and the complicated phrase structure. Imagine that you actually started to learn English about 4 years ago. Within a year I can tell you that you will be able to build an English vocabulary, without the slang, that would be comparable with that of any other less educated american. Then in the next few years, going to college, you start to add more, and more words to the vocabulary, become more proficient in English, etc. However, the level of English vocabulary proficiency that is required for the MCAT, the ESL person will not be able to achieve withing only 4 years of learning English.
Now why do they do better in the science portion of the MCAT? Simple, there are NO complicated words in that portion! Everything is simple, like "a ball is rolling on an incline..." or "find out the pH of a solution of ...". If you look at the verbal reasoning passages, there are a lot of words that are not used in everyday life, that are complicated for the ESL, because the ESL never heard them or read them before.
Now I speak fluently 4 languages, but please don't make me take the verbal reasoning in Spanish! Although I watch the Spanish TV channels and I can understand everything and I speak with my neighbors in Spanish without any american accent, I am not that proficient in Spanish to take a verbal test in that language. But, it would not be a problem to take the science part of the test in Spanish, because science is all the same regardless of the language, and one does not need complicated words to discribe the phenomena.
And for all the people out there that believe that knowing other languages is not important: What are you going to do when you get into a California school like UCSD or UCLA and find yourself with people that don't speak any English that you have to treat? What are you going to say? Hold on until the interpreter comes? Would you think that speaking another language is important then?
And by the way, this year in California the hispanic births outnumbered the white births, so pretty soon, if you want to visit California you will have to learn Spanish, and I would not be surprised if in 20 years from now the UCs are going to offer bilingual instruction. They already offer Spanish classes as part of the medical training.
I am sorry for the long post, but I could not believe that someone would actually claim that ESL is just an excuse for poor verbal score.