Divorce law in this country is seriously fucked-up.
Normally (in most states) alimony is seen as transitional and only lasts a limited time. If the marriage was very long (i.e. 20 years) and the woman was a home-maker for those 20 years (thus less employable), I think they get more.
To be an alimony for life issue, I wonder if it was part of the "equitable" distribution of the marriage assets. If, for example, a guy has a multi-million dollar privately-owned company, some judges will let him keep 100% of the company and pay an annuity for life instead.