Earlier quoted context omitted.
"Storing data in any application results in some restrictions [...]" - I think you understand her point pretty well.
No, he doesn't, and I don't too. How would that be different with any Open Source application? There is NO common interchange format for music information besides the embedded mp3 metadata. Of course iTunes (and ANY other player, OSS or not) has to store non-standard stuff outside those. And even if it stored them inside, there is no consensus about the naming and interoperability for metadata not in the standard lis…
In theory the Unix way is to have plain text as input and output. This has meant that many open source softwares use nice plain text files for their data storage stuff.