Of cource, when working out the relative times for rail and air, they fail to take into account check in times and time taken to get through the airport at the other end (oviously, that would vary if you have checked bagage or not). Then again, these sort of manipulations are often made by people trying to make one form of transport seem superior to others (and it's done for rail aswell). Also, whilst the trains might not be that reliable, the planes arn't 100% reliable either, especilly when flying to and from a busy airport like Gatwick. That said, it's noticable that trains often loose out in situations where the journey times for alternate modes are similar, with reliability being the issue, so it shows more needs to be done to improve reliability and punctuality.
Overall though, I'm not against domestic air travel by a long way, and whilst I've never done it myself, there are quite a few journies where I would use air were I to make them, and others where I would use air if flights were available (East Midlands, my local airport, only has Scottish destinations on the British mainland). I can see flights like Newquay to Gatwick being particularly useful for people wanting to travel to Gatwick (particularly the airport itself) or the surrounding area, including the south cost. One thing trains tend to be particularly poor for is journies requring crossing London, since this can add around an hour to the journey time, and isn't the easiest thing when travelling with lots of luggage, family or both, yet routes bypassing London are often very slow, and likely still involve quite a few changes.