Is this not a bias? As in: It only looks like Google discriminates for the Big Three, because they are so abundant?
I've heard from official sources like below that Google doesn't discriminate on TLD. There are my sites and Googlers who use ".info" TLD in a legit and well-ranking manner.
Where this "evidence" does play a role, is in spam/made for Adwords-sites. It is reasonable to assume that a .co or .ly will get more attention, to combat spam/made for Adwords sites that try to use Keyword-In-Domain tricks to outrank legit companies.
But if you are not making Keyword-In-Domain Made-For-Adwords sites, you have nothing to worry about (at least as for Google discrimination).
It is mostly _users_ who discriminate for a .com. If Google ranks website.ly in the top 5, but its users don't click on the result, in fear of spam or low-quality, then your rankings might suffer.
Matt Cutts interview on DomainRoundtable.
"For example, do .com domains carry more weight than a
.net, .us, .info, etc.
He said that TLD doesn’t matter -- that’s the way Larry
and Sergey originally designed the Google algorithm. The
algorithm doesn’t care where the page is located, it’s
all about pagerank (LINKS) of the particular page. At the
end of answering this question he did admit that they
might have started to look at particularly cheap (and
spammy) TLDs differently than other TLDs or they might
start considering TLD in their algorithm if they’re not
already doing so."
So it is still good to advice against .io and witty domain names (portfol.io), but not for the reason of Google discrimination.
I am reminded by statements like: "For better ranking, claim your domain for 5+ years". Just because Google gives extra attention to domains with a low expiration date, because they correlate with spammy/get-rich-quick sites, doesn't mean that spam on a 5+ years registered domain is ok, or that simply claiming a domain for 10 years, somehow signals quality to Google.
You only have to worry about registration dates, when you know that you deliver low-quality content and you don't want to be found out soon.