grasshopper wrote ('way back):
"With the self-taught finger-pickers they mostly seem to use the free stroke - which is limiting with an acoustic instrument, where you can't just adjust the tone control. ",
and twang wrote:
"...I find the steel strings less sensitive to technical nuances than my classical guitars..."
Practically all of differences between what we call 'classical' (nylon/gut string) and 'acoustic' (steel string) guitars stem from the differences in the strings. The major one has to do with 'damping': how quickly the energy is dissipated as the string vibrates, which has a lot to do with the basic timbre of the string. As a material, steel has much lower damping than nylon; a plate of steel can ring on for some time when it's been struck, while a similar piece of nylon just goes 'thud'. Steel is also much denser than nylon, so for a given tension a steel string is much thinner. This means that it doesn't have to move as much air as it vibrates. That sort of movement doesn't produce sound because the string is too thin to create a bulk pressure wave in the air. It's more like trying to run in knee-deep water; you don't so much produce a current as just get tired out.
One of the ways damping is measured is to look at the amplitude of the vibrating object over time. Basically, you count how many cycles of vibration it takes to cut the amplitude down by a certain amount; the fewer the cycles the faster the energy is being dissipated. If you think about it, what this says is that with high damping you tend to lose the high frequencies first: if the energy drops by half in, say, 100 cycles, it will take about a second for that to happen at G on the low E string, but only 1/10 second at the top C, 8th fret on the high E .The same holds true for all the overtones. If you record plucks of steel and nylon strings and analyze the energy at different frequencies, you'll find that a steel string can retain a lot of high frequency for several seconds, while a nylon string will have very little energy above, say, 4000 Hz after a second or so.
This has ramifications both for players and builders. One player I know, John Bigelow, put it very cogently: " The problem with trying to play classical music on a steel string guitar is that it's like listening to Julie Andrews in 'The Sound of Music': there's no darkness!" Much of the effort of learning both to build and to play nylon/gut strung guitars has to do with getting as much as you can from the small amount of high frequency energy there is in the strings. When you know how to do that, it gives you a wide palette of tones to work with, from the sort of default 'dark' fundamental tone of the strings to something nearly as 'bright' with overtones as a steel string guitar can get. Steel strings are 'bright' by definition, and much of the luthier's effort in making a good steel string is to get enough bass to balance that. That's one reason why steel strings tend to be bigger boxes. All of that high-end energy in the steel strings helps with things like 'projection', but works against the wide palette of tone colors that a good classical player uses. No matter how hard a player works at it, no steel string guitar can match that.