I would be interested to see what makes the Asian airlines different... it seems as though flight attendants there are usually younger and quite attractive.
I'd guess it's: competition due to being seen as a glamorous job leading to a stream of young, attractive new recruits + it not meeting such expectations + (at least in Japan) girls wanting to get married by 25 and, having English under their belt and a "desirable" job, achieving this goal and stepping down to be a salaryman's wife rather than staying on until they're "less hot".
So I doubt that the average stewardess is the type that is desperate to get married by 25 (which would likely imply marrying a guy who makes less than her!), though you have a point in that when they do get married they'll most likely retire.
(FWIW, I've never been on an AA flight where all the flight attendants seemed to be able to speak a language other than English, but every flight attendant I've seen on Cathay or Dragonair has been able to speak English and probably Cantonese, Mandarin, and Japanese as well. I always found it very interesting that people even bother flying US-based airlines.)
I think you underestimate the relative skills/responsibilities of flight attendants vs. female Japanese office workers. They former are trained in airplane security and first aid. The latter are just administrative assistants -- even the few ones that can speak English aren't trained to be translators, for instance.
For what is worth, I use US or Canada airlines because their Tokyo-N.America-Sao Paulo flights are way cheaper than the good Asian ones (as in U$1500 instead of $2000).
1. Flight attendants is a way for women to travel before assuming traditional domestic roles. Few of them plan to make a career of it and many see it as a way to meet well connected men. The last flight I took (BA) had a thai and japanese flight attendant. Both spoke many languages fluently and both worked for their national carriers at one point, Thai Airways and JAL. When they started getting too old (>40) they were both unceremoniously booted from the airline. They really enjoyed the time they worked there but were now starting from the bottom at another airline.
2. Customer service. US airlines have gotten much worse at it Asian airlines are doing an outstanding job. Take 200+ passengers that have had a relatively shitty experience of purchasing tickets, airport security, and delays. Now it's the job of 5-10 cabin crew to try and pacify them for the next 2-6 hours. It's a recipe for disaster for everyone involved.