try running path\to\VC\bin\vcvars32.bat from within your current shell first. This should ensure your command-line setup will match the IDE-setup.
This is not a permanent fix — you need to do it every time you launch a new shell.
You could probably also find some way to add everything that’s in that .bat permanently to the environment variables, but…. like you asked, why the heck doesn’t the MS install do that already?