“Two nations divided by a common language”

I very much enjoyed "Divided by a Common Language," about the differences between American and British English. Bryan A. Garner concluded it thus:

The differences between American and British English are tuned finely enough to carry tone, identity, and local flavor without blocking understanding. An American novelist who writes mom instead of mum summons a whole emotional landscape in three letters; a British narrator who chooses lorry over truck conjures a road running through a very different place. English remains gloriously mongrel, perfectly able to let both sides sound entirely themselves — and still, cheerfully, understand one another.

But then I came across this at the end of a book review in the Daily Telegraph:

This book is an entertaining read, but its thesis is overblown and exaggerated. It is also written in American [emphasis added], a language whose spellings and idioms are exceptionally irritating to British readers. Even if Allen Lane are short of editors, can’t they at least show sufficient respect for their British market to invest in some software that will translate such books into English?

I live in a place called the "Capitol Centre." I don't mind.