Yeah Lego is very different to TF's. As a buyer and seller in the last three years I've learnt that some people say BNIB (Brand new in bags) is not Brand new in box, but MISB is still Mint in sealed Box.
The reason for this is that some Lego collectors don't care about the box so they are happy with BNIB, but it's best to clarify with the seller before jumping in.
The advantage with Lego and the bigger sets buying without box but brand new in bags is obviously the postage price.