[vcg3rd]

The problem isn't the Oxford comma. The problem is lazy--or possibly rapid, if one is generous--writing and editing (if any). If the use or absence of a comma causes ambiguity, it's probably best to rewrite the sentence.

I believe it was Orwell who wrote a friend: "I am sorry this letter is so long. I didn't have time to make it shorter."

[GrumpySloth]

Blaise Pascal, several centuries earlier.

[gerdesj]

Well, if we are going to be authoritative then we might like to ... well:

"I believe it was Orwell who wrote [to] a friend: "

... soz, you are probably left pondian and have a habit of writing your friends. I like to get all transitive and write to mine.

[thaumasiotes]

> you are probably left pondian and have a habit of writing your friends. I like to get all transitive and write to mine.

"Writing your friends" is transitive; "writing to them" is intransitive.

[bennettbackward]

"I believe it was Orwell who wrote a friend [a letter]:"

It's perfectly correct and common to say "wrote a friend".