[QUOTE=Jurph]
Is it possible that there’s evolutionary pressure going on here? Attorney-type letters that are written well succeed, so they’re more likely to be reused or shared within the 419 community. A poorly-written “attorney” letter that gets almost no replies won’t be copied again.
[/quote]
As I’ve already mentioned, most attorney letters are not copied. In fact, although many have similar themes and general formats, I have very few letters in my collection that have sections that appear to be copied word-for-word. Although they always include some large sum of money that writer needs assistance in getting his hands on, sometimes the source is oil funds, sometimes it is some corrupt government deal, sometimes it is some foreigner who died without a will. (In one case I got a letter alleging that a foreigner who shared my real last name - a name that is extremely rare - had died in a car crash, and they were writing to me in the expectation that I was the next of kin.) Clearly, the English has been composed independently in most of them.
It may also be worth mentioning that, although most attorney letters contain a few errors, anyone gullible to believe such a letter in the first place is not going to be put off by a few apparent typos. Since they always come from a foreigner, it’s easy to dismiss them as the kind of mistakes even an educated person might make if their first language were not English.
Naive letters are also not copied word-for-word. They also have the theme of a large amount of money that the writer needs assistence in obtaining, but they are even more varied in content than attorney letters. Sometimes the writer is the widow or daughter of some merchant or official, usually killed by some corrupt regime (I have received letters from the widows of dictators, kings, and generals, not to mention the widow of Yasser Arafat), sometimes it is missionary that is seeking to disburse charitable donations, etc.
As you point out in your second sentence, although good English enhances the versimilitude of an attorney letter, it decreases the believability of a naive letter. Hence the differences seen between the two kinds of letters.
You would think if successful letters were shared or passed around, I would get multiple copies of very similar letters. While I occasionally do get duplicates or near-duplicates, this is uncommon. They generally vary quite a bit. (That’s one reason I collect them.)
For amusement, here’s another example from my collection. This one tells me I am a beneficiary of the will of former British Prime Minister Edward Hearth. While there are some typos and oddities of expression, the English itself is pretty good, and much better than the typical “naive” letter.