Mine arrived with 1 broken seal on one side and a half broken seal on the other. I didn't ask for my account to be be pre-sync'd or whatever, and it wasn't. It wasn't even me who purchased it as it was a gift from my mom. You could get it open with 1 broken seal, but everything looked intact and was clean, no finger prints, etc. It was a replacement for a N10 that was damaged during shipping and I had already waited way too long for a N10 so I didn't send it back. So far it has been fine.
Well, if your mom purchased it, how do you know the account sync option wasn't applied? I guess the fact that it wasn't already synced is good indicator...but just sayin'
I can say when I ordered mine I definitely did NOT choose the option to pre-load my account, and when it arrived last weekend, both tamper seals were intact, for what it's worth.
It would make sense that's what could be cause of it, but it's strange that there's more than a few folks here who had the seals broken who didn't opt for the account pre-load option. My only guess, assuming Google's explanation is correct, is that they got some over-ambitious folks running working at the distribution center that are assuming the device needs to be pre-loaded until after they've opened it and then realize that they don't need to and just send it off as is.