I suppose those posts might have the same ID if we didn't do anything else differently, but not sure.
For the imported posts, yes, they should have been the same. For the manually-duplicated posts, not necessarily so.
The standard WP.com importer is broken at best,
Your import file must have been really massive, then, or your server has limits that were too low for the job to function properly. In any case, since you're done, we won't troubleshoot that any further, the important thing is it's fixed!
It'd be awesome if someone would fix that importer so it doesn't just fail on a blank screen if you have a large site.
I found a Trac ticket that I think is related:
Feel free to add to that or follow it, or create a brand new ticket if you think this one isn't relevant.
OH and if there was some genius way of importing one's WP.com settings so that Jetpack is configured to basically duplicate those features, that'd be awesome too.
That's an interesting idea; which setting should be imported, though? Which ones would be valuable enough and are enough of a hassle that they would merit a user installing and/or manipulating a new module in Jetpack? I'm not being sarcastic, by the way, this is a legitimate question. :) I'd like to open a ticket about this but I'd need a bit more feedback from you about what would have made the process smoother for you. :)