The limitations of the backing up/restoring of database are more to do with limitations of the HTTP protocol implementation more than anything. There's a limit to how much mileage you can get with web forms and HTTP 1.0/1.1 with bigger files. Very true. As was said above, the best way is to use a c...
I know vB3 does that out of the box but I doubt the phpBB developers would see it as a necessity for a forum and I tend to agree. It would also be very easy to write as a mod so just wait for someone to write it, would take like 2 mins really.
I believe this is handled by the resync() function. I had a quick squiz at the code once and that function does everything. Pretty sure it sort out attachments as well.