I don't think Steam being 64bit stops you launching 32bit games, just reduces the need for all the 32bit dependencies to use Steam at all.

I'm in favor of removing 32-bit dependencies from steam-the-application, except that you still need 32-bit libraries to run 32-bit games in Wine.

Having steam depend on those libraries directly means that when you install you get all the libraries you'll need and you won't run into issues later on when you go to run a 32-bit game and it can't load the appropriate 32-bit system libraries for you. It's annoying for sure but it simplifies the user experience dramatically (especially if you're just installing Steam directly on Ubuntu or something).