the reason for the new mics probably isn't a cost issue but to make sure a 360 owner can walk in a store pic up a wired mic and have it work with their system -- no matter what the configuration.
the text messaging pad kind of screwed with this because it offsets the bottom of the pad by several inches, and it's no longer easily possible to twiddle the mute or volume with your thumb, and having that connector stand out past the basic shape would look and feel really clumsy.
that being said, i much prefer the older mics and i couldn't figure out why more 3rd parties didn't do mics with the little wedge + controls. i loved being able to easily mute myself to cough or sneeze or whatever and do this all simply and one-handed.
Edit: *beaten*
Edit2: gamestops usually carry a bunch of the old ones if you don't mind a used one. (some of them have probably never been worn)