Fair enough; your analogy is better. But not for the reason you point out.
Because FAT32 naming conventions are radically different from Linux', and because it supports radically different directory restrictions, and because it has attributes that Linux doesn't understand, and because it doesn't support permissions, I have to always keep clearly in mind when I've mounted a FAT32 volume v. basically anything else. Yes, I can mount it, and it works just fine until it doesn't.
This is my experience with hg-git. Mercurial tags can be moved, Git tags can't be, so I need to keep that in mind. Mercurial signatures don't map to Git ones for obvious reasons or vice-versa, so I can't actually figure out whether a given release was signed by the project author. Mercurial branches lack Git analogs, so I have to remember not to use them. Mercurial bookmarks map to Git branches, so I have to be ready for bookmarks to move in odd ways as Git users work with my hg-git repository. Mercurial's multiple heads per branch have no real analog in Git (they'd be up for garbage collection). This list goes on.
When I use hg-git, I have to always keep the Git model in my head, AND keep the Mercurial model in my head, AND keep in mind how those two models interact. This isn't fun, and it's not anything remotely close to transparent. It's amazingly impressive how well hg-git works, but claiming that GitHub supports Mercurial due to hg-git is horribly misleading.
Because FAT32 naming conventions are radically different from Linux', and because it supports radically different directory restrictions, and because it has attributes that Linux doesn't understand, and because it doesn't support permissions, I have to always keep clearly in mind when I've mounted a FAT32 volume v. basically anything else. Yes, I can mount it, and it works just fine until it doesn't.
This is my experience with hg-git. Mercurial tags can be moved, Git tags can't be, so I need to keep that in mind. Mercurial signatures don't map to Git ones for obvious reasons or vice-versa, so I can't actually figure out whether a given release was signed by the project author. Mercurial branches lack Git analogs, so I have to remember not to use them. Mercurial bookmarks map to Git branches, so I have to be ready for bookmarks to move in odd ways as Git users work with my hg-git repository. Mercurial's multiple heads per branch have no real analog in Git (they'd be up for garbage collection). This list goes on.
When I use hg-git, I have to always keep the Git model in my head, AND keep the Mercurial model in my head, AND keep in mind how those two models interact. This isn't fun, and it's not anything remotely close to transparent. It's amazingly impressive how well hg-git works, but claiming that GitHub supports Mercurial due to hg-git is horribly misleading.