Quick question, who are the "Big-4"? I count Google, Facebook, Apple, Amazon, and Microsoft at a minimum.
It came from accounting/consulting where there are four really big consulting giants: (KPMG, Earnst & Young, Pricewaterhouse Coopers, and Deloitte). Interestingly enough, the above aren't known for being particularly nice employers.
On the sub the inclusion in the "big four" varies a bit, Google is the only one who's always in it. Others sometimes included are Microsoft, Facebook, Twitter, Amazon, and Adobe.
[1] http://www.techrepublic.com/blog/tech-sanity-check/schmidt-c...
https://en.wikipedia.org/wiki/Big_Four_%28audit_firms%29
However, if we look at the disambiguation, we find at the bottom of the subsection:
https://en.wikipedia.org/wiki/Big_Four#Companies
"Big Four, the most influential international technology companies Amazon.com, Apple Inc, Facebook and Google".
So I'd say it's pretty ambiguous.