But you only have to give the offer to whomever you give the object/executable to. So you tell them "you can get the source from foo://bar.baz/phaf" ... this just has to be a publically accessible address with no additional authentication or authorization. You are not required to announce this in any way other than in the written offer which accompanies the object/executable.
So, although in theory any third party has access to the source code, you are not being required to put it in a publically visible location, merely a publically accessible one.
[EDIT: I was saying that GPLv3 also does not have transitivity,so we agree about that ]
[EDIT: I admit that I am misleading in my final sentence ... yes, any third party has the right to access the source code, but you are not required to notify "any third party" of this fact, only those you gave the object/executable to. ]
> b) Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,
GPLv3 has transitivity not GPLv2, but GPLv2 doesn't need it because it already specified any 3rd party.
Edit: Reread what you wrote, GPLv3 b (i.e. written offers) has transitivity, I do think that GPLv3 d does not (but does distribute the source simultaneously with the binary in some sense).