Sorry, but microSD cards do not help with a positive user experience for "most" users. Excluding, you, me, and a handful of others that is. Failing cards, digging inside of phones, hard resets, losing all data, are not things that Microsoft wants to associate with WP.
I will agree that 32GB models would go a long way in making many users happy, at an increased cost of course. But that won't happen till overall WP increases so it can be cost justified at the manufacturing level. Maybe next year.
Sent from my Lumia 900 using Board Express