Kev - I think they said 'primarily' rather than 'very much'. That may seem mere semantics, but makes a difference. The former is nothing more than a statement of fact which refers to the commemorations rather than representing a view that the Normandy campaign was primarily a Franco-American affair.
The government (ours) decided that it would not participate fully in the 65th anniversary ceremonies, which meant that the events would have been an
entirely Franco-American affair (in the sense of official representation) until events overtook HMG.
It appears that the PM said in March that he would attend a commemoration at Caen in a bit of a climb-down from the original 'no official recognition' position:
Link
Note that the PM's spokesman thought only in terms of heads of government, rather than heads of state - one suspects that the French assumed that the invitation they despatched would see HMQ appear, representing the UK and Canada (and the Aussies and Kiwis who participated in the air aspects of the Normandy campaign) as you get four heads of state in one with that invitation.
I would go so far as to suggest that the French are probably rather horrified at the fact that the inept handling of the invitation means that we have two heads of state and a head of government (who may wish to be out of the country on 5th June...) leaving one key nation in the invasion force with no head of state/head of govt representation at all...
The Mail's usual eagerness to have a pop at our cross channel neighbours has, I would contend, let Mr Brown somewhat off the hook since it seems most probable that no snub was intended. In that scenario, this farago is all down to the failure (unwillingness??) in Downing Street to comprehend that while Messrs Sarkozy and Obama are both heads of state and of government, Mr Brown is not, and someone in his organisation should've ensured that HMQ was at least asked if she wished to go.