They are, and I'm sure there's floating plants where neons come from in the wild too .
My guess is that they are just resting in the plants because they are ill, and then dying.
Are the neons new additions to the tank?
What are your water stats?
What are the rest of your water stat's? Nitrite, Amonia and Nitrate? Ph is not really a problem unless your water is excessively acidic or alkaline, I only test mine every month or so, when they re-dose the water with whatever it is that makes it smell and taste foul but apparently makes it safe to drink! Needless to say we don't, we have tanks for our drinking and cooking water.
It kind of sounds like you haven't had the tank very long. Was it fully cycled before you added the fish? If it wasn't that would explain the Neon's dying first, followed by the guppy, which will most likely be followed by the gourami!