Are you kidding me? The whole reason that Square ever pursued the online gaming market in the first place was because they were nearly bankrupt from their endeavors with the Spirits Within.
As far as I'm concerned, it's absolutely ridiculous to expect Square to take a loss on FFXI just because they make money elsewhere. Think like a business-minded individual and try and justify that for me.
Further, the problem with charging for expansions only is that expansions--usually--are released rather infrequently. I'd rather pay a monthly fee and get the version updates and regular tweeks and fixes in place of one expansion pack every year and a half to two years.