So I've noticed this, and can't precisely explain whats happening, so I'm open to viewpoints. Basically, if you take any electric or pickup-ed guitar and run it through a line-in, direct input, etc. vs. Taking a send from that same guitar through an amplifier, even a 10 watt practice amp or anything, You'll find some really smooth, lower-ratio compression (and some equalizing that will make the general tone better and could prove tricky in listening for compression) coming from the amplifier. I could bullshit you about how tube saturation contains a natural soft-knee compression, and solid state amps emulate this, but I haven't found any solid explanations of this, and would be interested in any further information.