Does a ResearchGate profile count as a "personal website" for green OA purposes?
The 2009 blog post you linked to makes the claim that
each profile page within ResearchGATE is legally considered the personal website of the user
Similar claims had been made by Academia.edu and Mendeley, according to Michael Clarke at the blog Scholarly Kitchen. He elaborates on these claims following an incident in 2013 in which Elsevier sent large numbers of DMCA takedown requests to Academia.edu:
William Gunn [of Mendeley] puts forth an argument that Mendeley has long used for hosting content they do not have explicit permission from rights holders to host: that an individual’s profile page on Mendeley (or by extension, Academia.edu) is that individual’s “personal website” and therefore covered under the exemption that many publishers provide to authors in both copyright and exclusive licensing agreements, allowing authors to post PDFs of their work to their own personal or institutional (e.g. their laboratory or departmental) website. Since papers are loaded to both Mendeley and Academia.edu by authors, the argument is that the paper is “self-archived” to the author’s personal website.
Leaving aside the fact that many publishers permit only the author’s accepted manuscript (and not the final PDF) to be self-archived, were one to accept this argument, by logical extension this would mean any commercial site (Academia.edu, ResearchGate, Facebook, LinkedIn, Scribd, Google, etc.) that sets up a profile page would have the right to host any research loaded to the site by an author. The distinction between a profile page on an academic or professional network and a personal or institutional website does not strike me as difficult to make and if it were ever an open question, as Mr. Gunn asserts, the question seems to have just been answered by the legal department of his own employer.
More recently, some publishers have begun to explicitly specify authors' rights regarding posting on sites like ResearchGate, and that these are different from authors' rights regarding posting on personal web pages. For example AIP defines
Within a commercial scholarly collaboration network (SCN) site:
An SCN is a professional networking site that facilitates collaboration among researchers as well as the sharing of data, results, and publications. SCNs include, for example, sites such as Academia.edu, ResearchGate, and Mendeley, among others.
as a separate category from "authors’ personal web page and employers’ web page".
I'd say that a key distinguishing characteristic of a "personal website" is that it can be considered non commercial.
ResearchGate is a company and uses the papers uploaded for commercial purposes such as recruitment.
The example journal in the link you provide is from Elsevier. As you can see the post-print (the post-review pre-print) should come with a CC-BY-NC-ND license -- that is only Non-Commercial use is allowed.
This means uploading to a commercial repository such as ResearchGate is not permitted as it does not meet the non-commercial aspect of a personal web site.
Note that many publishers, not just Elsevier, explicitly forbid sharing post-prints on commercial repositories.