The three steels do contain different amounts of carbon. They also contain different amounts of other elements that are used to make steels. 1095 is simply .95% carbon and no other trace elements. SR-77 and 101 are steels that contain other elements and a different amount of carbon (less). Carbon is what makes steel hard. More carbon equals harder steel but the trade-off is that as it gets harder it becomes more brittle. SR-77 is a variation of the S-7 spring steel and is low carbon - which equates to a softer steel but much tougher. The special heat treatment given to it by SY adds to its edge holding abilities.
I'm sure KG can offer more on this.

I'm currently trying to figure out what steel to try and make my first custom knife out of..And its not an easy choice. I'm thinking 1080, O-1 or 440-C.
Any suggestions/thoughts?