In my experience, Air France does the following for all US-bound flights:
1. ICTS/Securicor interview prior to check-in
2. Random hand inspection of checked bags
3. Passport and boarding pass check at gate. Provision of US entry documents.
4. Random or less-than-random pat downs and shoe inspections for some flights. Sometimes it's all male passengers (I'm not kidding.), sometimes it's every 4th or 5th passenger, sometimes it's totally random.

The US carriers at Charles de Gaulle:
1. ICTS interview prior to check in
2. Random or non-random inspection of checked bags
3. Second interview and document inspection prior to boarding.
4. Random or less-than-random VERY THOROUGH pat downs and bag inspections, first with wand and then without, including hair inspection, shoe inspection, and detailed inspection of hand baggage.

And--I agree-things seem to be MUCH more thorough at Gatwick than Heathrow. I can't imagine why.