Seriously? A 9am flight from London should need an overnight stay at the airport? Many hotels which market themselves as hotels for Gatwick are no quicker (or longer) to the airport than the 30 minutes it's supposed to take from Victoria. The last time I flew from Gatwick was to Jersey, a 30 minute flight after a 15 minute train journey from East Croydon. My "risk assessment" was getting an earlier train than I could have. I didn't have the common sense approach to book an airport hotel for the return journey either.
Yes.
A 9am flight means generally 8am check-in at the latest at Heathrow/Gatwick, so you should aim to get there for 7am, as most sensible people would, as a minimum. Throw in some insurance and you are looking at planning to get there for 6-6.30am.
All it takes is a small accident on the way and you run the risk of cutting it really fine. Many people seem to think that things would go to plan as long as they take the one train ahead. It may well do in the majority of cases, but many also rapidly change their opinion after just one encounter with a bigger incident. The impact of this incident is actually quite mild in comparison. Throw in a fatality or a broken rail somewhere and you could easily pick up 80/90+ minutes delay.
A lot of what you want to do will partly depend on how important it is for you to be on that flight. If you can afford to miss the flight and go on the one a few hours later (if you have an alternative, perhaps in a different mode altogether even), possibly for a fee just for yourself, then fine, take your chances, but if you were taking your family to Cannes, which is hardly the easiest place to get to and possibly having to shell out additional charges for several people, or Tobago even, as are the two cases quoted in the article, that is terrible planning IMO. Not many people taking flights at Gatwick early morning on a Sunday are going to be those in suits heading for a business meeting, and most leisure destinations aren't known for having several flights a day which you can switch easily between.
The advantage of hotels nearby is that they are mostly a short ride away in a taxi, or on a shuttle bus, or even within walking distance, so you have plenty of options in the morning, and not subject to the unpredictability of a longer journey, even if they may be scheduled to take a similar amount of time. In any case, if you end up in a hotel a 30-minute ride away from the airport, you need to do better as there is almost certainly a more convenient one around. I would urge anyone doing that to do their research and confirm their options beforehand.
The journey home is irrelevant.
If people want to go in the morning and relying on the only 1/2/3 trains that could get them there in time, no problem, just people shouldn't then be surprised when things go pear-shaped, because as they say, such is life. Staying close to the airport would in comparison reduce the probability of being impacted by events not within one's control to the minimum.