This is one drawback of iOS's lack of a user accessible file system.
It's only a 'drawback' if you refuse to use a modern workflow. There are numerous ways to get a file from your phone to your mac or pc, without plugging in a cable. Email, cloud storage, airplay, wi-fi sd card readers...
I find it more convenient to just upload whatever file I need to dropbox or google drive. I don't even carry around my 8GB USB flash drive anymore.
It would be nice. And it's totally possible. If it wasn't there'd be no way iTunes could sync or other third party apps could partially access the file system.Which is great unless it's a really big file and you have limited cloud storage or slow/limited wifi. Having the option of simple drag-and-drop via USB would be nice.
...USB would be nice.