Not to support the "evil executives" hypothesis---obvious market(ing) forces are a sufficient explanation for the dominance of LiCoO2---but I would easily opt for a laptop that offered an LiFePO4 ("iron phosphate" [0]) option. The drawback would be slightly reduced initial capacity; the advantage would be much greater cycle life. Also, less spontaneous combustion.
is it possible the better batteries don't (generally) exist because the manufacturers are not motivated to invest the r&d in the first place? i certainly have had too many laptops that don't provide optimum cooling (and they could, at more expense) when we know heat is a limiter of battery life.