Which titles in particular did you notice in the Kelson books that were held directly by women? I'll admit I can't think of any off-hand, but I might just not have noticed.
In our own world, inheritance does vary by country. From my own interest in medieval England/Wales, I know that England inherited by primogeniture (the eldest legitimate son got everything), while Wales divided land equally among all acknowledged sons (regardless of legitmacy). English heiresses (and their husbands) could inherit, but Welshwomen couldn't. According to Sharon Kay Penman (a writer of this time, who's a good researcher), women and handicapped men couldn't inherit in Wales because of fears they couldn't defend their lands from attack.
This could offer an explanation for Alyce's situation. Corwyn sat on the border with Torenth, and as the raiders in ITKS proved, it wasn't going to be too difficult for Torenthi raiders, or the Torenthi army, to try to invade there if they really wanted to. In matters where physical strength, or military action were involved, men were going to be viewed as superior and preferable. Perhaps this requirement was set up when Corwyn became part of Gwynedd, to keep the title in the original bloodline, rather than a man marrying the heiress for the title, she dies childless, he remarries and passes the title on to the son of his 2nd marriage (meaning no blood connection to the previous ruling line). Also might be connected to the de Corwyn line being Deryni, something often useful to the Haldane kings.
And in the Deryni world, there was a mixture of inheritance styles: the Lowlands used primogeniture, and the border regions appear to have used a mixture of primogeniture and tanistry (where the most qualified candidate inherits). Like how Dhugal automatically got the Earldom of Transha because he was thought to be Earl Cauley's son, but it wasn't as certain that he would get the chieftanship. As Ciard said, Dhugal could have been chosen as the next chief even if he hadn't been a blood relative of Cauley.