Mint 17.1 users will not see the popup, because for Mint 17.1 the Linux Mint repos
offer the virtualbox-guest-* software packages 4.3.18-dfsg-1~ubuntu1~trusty1, thus overriding any newer version offered by the Ubuntu repos. As a result users of Mint 17.1 will not be offered the upgrade to verson 4.3.34-dfsg-1+deb8u1ubuntu1.14.04.1 at this point in time.
Why this is only true for Mint 17.1, but not for Mint 17 and Mint 17.2, I do not know.
Confirmed - and really strange.
Some additions: The maintainers of those packages are different in the 17.x branch.
In LM 17 and LM 17.1 they are: Ubuntu Developers <firstname.lastname@example.org
In LM 17.1 and also in LM 17.3 Beta they are Debian Virtualbox Team <email@example.com
Also: In LM 17.3 Beta a newer version (5.0.4) gets offered. (Only as a side-note for completeness.)
So I add the question: Why different maintainers, although the base Ubuntu 14.04 is the same? No PPA is used in the named systems, all running in VMs.
Obviously one part of the answer is the fact, that for Rebecca and Rosa those packages are in the Mint repos, in Qiana and Rafaela they are not. But why: Intentionally (in this case again: why?) or (at least in case of Rafaela) forgotten?
At least the verdict is there, that there is a possible bug in the packages from Ubuntu Developers (affecting only Mint, not Ubuntu?). At least doing some search in the web does not seem to indicate, that there are problems for Ubuntu users, so I tent to believe, that the problem does only affect Mint (probably also other Ubuntu-based distros).
At now every investigation to find answers produces new questions.
So most likely users of Rosa will possibly also not be affected (probably depending, how 5.0.4 behaves). I have 17.3 installed in a virtual machine, so I cannot test it.
If the relating with the Maintainers should really be the culprit, I would expect, that also LMDE is not affected. I don't use it, but I would expect, that the maintainers are here also Debian Virtualbox Team.