That's true 99.9999999% of the time.
I've actually had a couple of non-sealed/non-new games show up from Gamestop.com, though it's been years since that happened.
These days, I'd be shocked if it wasn't new and sealed.
Back a few months when GS.com was selling SFIV for $19.99, I got gutted copies... TWICE. My friend, who ordered one at about the same time, got a sealed copy. I wasn't so lucky.
I told them what happened, sent the 1st one back for an exchange, and received a gutted copy the 2nd time around. I called to complain again and told them to send me a sealed copy and they said they would... again. I waited a week or two but didn't see anything in the mail so I gave them yet another call. It turns out they accidentally processed my 2nd exchange as a return, without telling me, and that it would be impossible to send me a copy at the $19.99 price. So, yes, they still do send gutted copies nowadays. I thought they didn't do this, either. I hate GameStop.