Distance from LHR to Paddington or LGW to Victoria is a ridiculous comparison. Nor are false comparisons of the costs of that trip helpful. Anyone paying £33 for the GEX to Victoria needs their head - and sense of priorities - examining.
You need to validly compare the distance to your end point and LGW is better placed for central and east London (and other places in the UK) than LHR.
There was a thread recently on the BA Board about why BA didn't operate flights from Jersey to LHR but did to LGW because "It's loaded with status passengers and those willing to pay for Club Europe so they should go to LHR because of that". The reason why is because the vast majority of passengers were headed to the finance houses in the City and LGW was quicker and easier for them to get to from LGW than LHR.