Bill,
I'll second what Bruce said about the aft end of the keel. It is indeed a false keel, if you will, that fairs out the trailing end. WHy it cracked...mmmmmmm, not sure, except that maybe it was blocked at one time with the weight of the boat resting on that last foot or so of the keel. If the boat is a deep keel (Non-C/B), then perhaps it had a hard grounding at one time which torqued the keel stub a bit.
As far as the skeg is concernced: This skeg is primarily used as a protective device for the rudder and to aid in tracking. It is totally hollow and does not support the rudder at all. The rudder has a pintle that you can see, mid way up the rudder and the skeg is bolted to the hull by way of the pintle. The skeg is removable when you take off the rudder. By the way, your rudder is most likely saturated unless a previous owner repaired it. Not a hard repair, but may affect your final offer......
By the way, the bottom half of the rudder as well as the skeg is designed to shear off in case of a really hard grounding leaving the top half of the rudder for steerage......ideally.......I haven't heard of anyone testing this out though
Cheers,
Tom