I transferred from a domestic BA flight arriving in T5 to an AA flight to LAX departing T3 yesterday. Prior to security in T3 I was directed to the AA transfer desks to get an AA boarding pass.
I was expecting the usual 'how long have you owned these bags' style questions, but instead was asked about who my employer was, where their HQ is, what the CEO's name was etc etc. I was even asked who I was hiring a car with in LAX. Basically much more intensive questioning than I've ever got at the US boarder. Is this normal now? I was quite taken aback by volume and detail of the questions, especially since there was no prior warning that there was going to be so many.
What is the point of this screening anyway, if you take a BA flight they don't ask you anything like this?
The questioning is required of US carriers flying to the US. As you say, foreign carriers flying to the US do not seem to be required to do this.
A cynic might suggest that the point of the screening is to look tough and reassuring.