Finder was rewritten because Apple is aggressively moving to 64-bit code which means Cocoa, not Carbon. Despite such extensive changes, the Finder (as seen by the user) arguably changed less than it had in any previous upgrade.
Similarly, iPhone and iPad deal with files one way or the other, but the point isn't how it works underneath -- you could have a team rewrite iPhone OS to use Newton-style "soups" and have essentially no change to the user's experience. Files are a convenient abstraction for programmers (and, remember, an abstraction is all they are -- in the end, disks are just a linear stream of bits that the kernel/file system layer "artificially" organize into "files"), and there doesn't seem to be any need to hide a file system from programmers. But users are, in most cases, better off dealing with app-specific document managers.
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Finder was rewritten because Apple is aggressively moving to 64-bit code which means Cocoa, not Carbon. Despite such extensive changes, the Finder (as seen by the user) arguably changed less than it had in any previous upgrade.
Similarly, iPhone and iPad deal with files one way or the other, but the point isn't how it works underneath -- you could have a team rewrite iPhone OS to use Newton-style "soups" and have essentially no change to the user's experience. Files are a convenient abstraction for programmers (and, remember, an abstraction is all they are -- in the end, disks are just a linear stream of bits that the kernel/file system layer "artificially" organize into "files"), and there doesn't seem to be any need to hide a file system from programmers. But users are, in most cases, better off dealing with app-specific document managers.