There is still some functionality that I prefer the standalone over studio version for, for example reloading an active plugin that I have saved changes to in an external editor. It might exist, but if it does I don't know how to do it without deleting the plugin, reloading it, and reconnecting the IO. Also I often see GUI inconsistencies in the studio version, particularly with dropboxes (tho I am probably slightly behind current, it may have been fixed).
Personally, I prefer the standalone over studio hands down for the initial writing and developing, but am starting to really appreciate studio when it comes time to test and debug. Studio is very handy in being able to patch in sound files to test with, or route the same audio to different versions of the plugins, and test how they react in real time.
It may not apply to everyone, but every cabbage instrument I write is with the intention of exporting it as a vst to be used in a larger DAW system... so the studio is neat but adds a lot of overhead and functionality that I just don't need 99% of the time.
Just my two cents