Are USB cables device-specific?
Solution 1:
The U means universal indeed, but some manufacturers (such as Apple) choose to provide their own proprietary USB cables -- which are not interchangeable -- while others provide generic USB cables which are interchangeable.
All standard USB connectors by pinout.
In picture form: micro USB on the left, then mini USB, then regular full-size B and A USB.
Solution 2:
The U in USB means Universal. They're totally interchangeable. I just keep one around and the rest as backups/to lend to others, it works pretty well.