Because Drive does not have access to your computer's file system, you have to make the call from your computer using the Drive API.
Here is a javascript example using Node:
Download a single file:
var fileId = '0BwwA4oUTeiV1UVNwOHItT0xfa2M';
var dest = fs.createWriteStream('/tmp/photo.jpg');
drive.files.get({
fileId: fileId,
alt: 'media'
})
.on('end', function () {
console.log('Done');
})
.on('error', function (err) {
console.log('Error during download', err);
})
.pipe(dest);
That should point you in the right direction and hopefully explain the limitations.