Geez...I think Neons are a lot tougher than that. When I was still in grade school and I didn't keep a good tank, the last fish to die in my tank were the Neons...they outlasted the Catfish even. I had no idea how to tend the tank properly. I didn't even have a heater in the water! So do look after your tank but I don't think the little pint sized blue and red suckers are fragile. They are also cheap so I heartily agree that you should buy them by the dozen or more. I have a school of 36. They have been around as an aquarium species for a long time. Ubiquitous they may be, but they are an endearing and cool little fish.
I think that Neons are like people, certain ones can withstand certain water conditions, others cannot. I had a 40 liter eclipse with only Neons. Their water conditions were slightly acidic and I had four batches of fry from them! They never got sick, and really grew to be rather large for their size.
I agree with Craeg on the Neons. While I currently do not own any (or any fish, I setup my first tank in 10 years yesterday), I have helped my girlfriend with her now 2 month old tank. She's had a lot of hard luck starting out, like horrible nitrate levels and when a defective heater got a few fish. However, the Neons have toughened through everything without showing any signs of stress. They went from 25 to 30 to 24°C in a matter of a few hours and were still chasing each other around the tank and fed normally. They are the first fish I plan on stocking my new tank with and from what I have witnessed I would recommend them to anyone else.
Make sure that if you are adding neon's to a tank with large angels that you acclimatize them in a breeding container/net for a substantial amount of time because a dazed or confused neon that is swimming lazily at the surface of the water due to pH or temperature shock will be very easy prey to a large angel or any other fin nippers for that matter, i.e, small nuisance tiger barbs. Last week my large angel managed to wipe out about 4 of my newly added neon's because the were a bit dazed at their new conditions. I separated the others straight away and they are perfectly fine now. Once they are acclimatized, they are perfectly aware of the angel's whereabouts and swim around very happily.
I adore these little guys. Many people say they are sensitive, but I have not experienced this at all. My neons have all been as tough as little red, blue and silver nails! I prefer them to cardinals because of the silver on their undersides. It gives them more shimmer. I don't think any tank is complete without a school of neons in it, unfortunately, they are seen as snacks by some larger fish. For this reason, they should only be kept in peaceful tanks with smaller-sized fish. They are very easy to feed, and take to flake or live & frozen foods readily.
I have 9 neons in my 200 L tank and 6 months ago I introduced 6 cardinal tetras. The neons are generally peaceful, but I have noticed that they pick on the cardinals; chasing and nipping at their fins. Usually the cardinals try to shoal or swim away, but the neons always continue their pursuit. At present, no cardinals have died - I believe the neons get bored with their game. From my experience, I have seen that the neon is far more confident when kept in groups of 6 of more to the point that they do not shoal anymore. If you intend on keeping neons with cardinals, I recommend you have equal numbers for both species, if not more for the cardinals, because my cardinals seem less boisterous than the neons.