Okay. Joint in the debate I would have to say that even though I learnt English as a second language, I write it better than my native language. It just happened. I prefer speaking in my native language, but I write better English than my native language. Sigh.
I think this has a lot to do with the fact that English is bossy. It doesn't beg you to learn it, commands you to learn it. There are a lot of influences around that forced me to learn English. I had a wide range of English media available to me which facilities easy learning. The same, can't be said for Spanish which I am trying to learn.
So to answer Canuk's question, I think it's because English has basic structure, which if gotten right, comprehension can be achieved even if grammar rules and punctuation rules are thrown to the wind. I appreciate this point because my native language has more than 50 dialects, each with its own tone, accent and whatnot, but essentially, everybody understands everybody once they get the basics right.