Has the present perfect gone missing?

Guy Keleny, writing the Errors & Omissions column for the Independent, declares that those slovenly Americans are stealing the present perfect tense from the English language. He objects to a usage in his own paper: "Rather than meeting up and talking about what we want to post online, we just add to what someone – maybe on the other side of the world – already wrote."

From this slender evidence he generalizes sweepingly:

Any time up to about 10 years ago any British writer would have said "add to what someone has already written" [my italics].

Under the influence of American usage, the present perfect form of the verb ("has written") is losing ground to the past simple ("wrote"). In British English, the past simple merely signifies an action in the past, whereas the present perfect describes a state of affairs in the present brought about by an action in the past – we now are in a world where somebody "has written". American English, with only the past simple to call on, fails to mark that distinction.

Have you noticed the disappearance of the present perfect in American English? I have not – though of course I've seen "he wrote" in casual contexts where more formal prose would call for "he has written." Is the present perfect really "distinctively British," as Keleny's headline claims? Is its use diminishing in British English, and if so, is it Americans' fault? I'm not good enough at Zimmering* to test these assertions properly (and I'm about to be off the grid for a bit), but perhaps one of the adepts – Mark Liberman or Ben Zimmer himself – can show me how it's done.

Or maybe Keleny will reveal his evidence. But I suspect his lamentation is based on mere sentiment, seasoned with a dash of prejudice. 

*"Wait, I'm not ready to be an eponym!" Zimmer tweeted in response to this coinage. Too late, Ben!