I still don't see the "fundamental flaw". Non-reachable commits are automatically deleted by the garbage collection system, which can be also be run manually. Accidental commits with large files or private content can be "modified" (technically copied and rewritten, since individual commits are immutable) with rebase, amend, filter-branch, etc. Those operations make the original commits unreachable, so garbage collection takes care of deleting them.
And like I already said above, data loss can occur when you're working with uncommitted changes, just like in most other version control systems. If the content is not under version control (in this case, not in a git commit), it's not safe.
Honestly, you guys should go watch Linus Torvalds' presentation at Google about Git. The entire point, the massive problem he was trying to solve, was preservation and verification of data integrity.
