@Dobbo Dobbo well yes, not a secret. It does much better in terms of %business per flight and yield than say LGW or MAN which is why airlines pay silly money to get slots.
e.g. China Airlines relaunching London on the A359 out of Gatwick with
PR stating they are actively seeking LHR slots for 2018. Why? Beacause LHR is preferred to LGW on long haul business. Emirates fly high Y A380s out of LGW but not LHR. The fact that most people are going on hols in terms of % throughput is secondary to the ability to charge more in the front cabins due to market preference.
LHR DOES have business credentials in a way LGW lacks in exactly the same way MAN has over say LPL or LBA. Some good points though from posters!