Experience plays a good part. A good rod helps of course. Even with mono, I can differentiate (at least I believe so) between mud, grass, wood, rocks and bass. I fish a wide spectrum of rods too. $275 GGRs (phenix blanks I think, pretty much a top of the line rod anyway), $170 Powells, down to $100 Okumas and Shimano Compres. The difference between the rods are in the crispness- for lack of a better word- of detecting the cover/structure/bite. Almost always, I have a finger on the blank too.
P.S. I had a memorable bite two weeks back. I casted out a little 3/16 oz jig on 30 lb braid, and I let it sink on slack line (I watch the line, and prefer the bait to fall straight down vertically). I didn't even have a finger on the blank since I had just casted it out. I FELT a tick (braid has very little sensitivity on slack line), reeled up, and set the hook on a 6" (inch) bass.
The rod was a Powell Max 733 spinning.