What I miss:
-Pokemon walking after you
-VS seeker
-The possiblity to use TM's more than once
-Seasons
Along with the rest of these dogs here I miss when my Pokemon would follow me. I also really liked the VS seeker and I think it should be brought back.
The reason Pokemon following you is actually justified.
B&W were in development about the same time as Platinum.
Now anyone who has done any form of Hacking into the scripts of HGSS know that every script has to move the Player, and the Pokemon, and the game crashes if any OW entity tries to walk over either person.
Now, since the Games were in development around Platinum (wich was before HGSS), it's safe to assume all the scripts had been made already. To last-minute insert the 'Follow Me' Pokemon from HGSS would take a long time, as every script would have to be re-written (BW has a ton of scripts, since map movement is scripted too). That would probally have pushed the Game's release back another month or so.
I'm betting dollars to doughnuts they have all the OW sprites, and have every intention of inserting them in Grey, as they have more time to work with the scripts.