iOS does it becuase it makes life easier.
android should have had it long ago.
at this point, i think its part of custom manufacturer themes (like sense) and its probably incorporated deep into the framework, hard to port over. like the music apk of touchwiz and other apps people have been asking about.
IF it can be ported, or created from scratch, it will probably be put in MIUI (there big on the iOS look)
If it was a standard feature of android 4.0, it would be back ported into CM7, but i dont think it is, so it wont. Rotation animations were backported though and are now a standard feature of CM7.
all in all, i dont think well see that zoom feature in a rom any day soon.
although i do agree it would be awesome to have