That's part of it. But also, if you start with a 4-patch series, and you want to publish a v2 that's changed to a 3-patch series, Gerrit doesn't seem to handle that very well. In general, I'd prefer if patches are kept together in one review, rather than a separate review for each.
Gerrit handles this perfectly - you can just add the third commit to your stack (and even amend the earlier ones) and it works as expected, adding it to the relation chain.
