Looking at the first page of the most successful Web-based startups of the last 10 years (e.g., Facebook, Instagram, Twitter), we see the extensive usage of the color blue. In terms of the graphic design, is there any technical meaning behind the color blue (e.g., social interaction, trust, 'coolness')?; or is it just a coincidence?
According to Google, blue is:
Blue is the color of the sky and sea. It is often associated with depth and stability. It symbolizes trust, loyalty, wisdom, confidence, intelligence, faith, truth, and heaven. Blue is considered beneficial to the mind and body.
All good things, and generally things that companies want to be associated with. Here is a neat article that's asking the exact question as you. Why do so many brands use Blue as their base colour?
The article looks at a study done by Emblemetric that traced the colors used in brands since the 90's. The study found that red had the lead in "most used color" until recently (about 2005), when blue overtook it. The author notes that while red denotes "passion and love", it also denotes "war and danger", things that social media (and other internet based companies) companies want to avoid.
Denoting power was something that companies wanted to do in the 90's to make people want their stocks. They largely ran operations behind closed doors, which was all well and good up until the internet came around. Now people could share the horror stories and companies can't sweep these reports under the rug. They're losing power, which is a red attribute. Now companies would rather show trustworthiness, loyalty, confidence, intelligence, truthfulness, stability and wisdom, all blue traits.
The internet is forcing new, more honest traits on companies, and the companies want to denote these traits to their customers as much as possible. Which is why so many of them are using blue as a base color.
It's a reflection that a lot of logos are blue is all. Blues and Reds tend to be the popular colors these days. And, really, they've been popular colors for logos for a long time.
In addition, I'm not sure what you define as a successful web startup, but note that today's startup world is mostly a bunch of people pumping out as many ideas as they can as fast as they can hoping one of them sticks. There's not necessarily a ton of thought going into these brands identities out of the gate. A lot of it is 'copy the last successful idea and then move on to the next'.
I'm not saying there's plagiarism or anything like that, but there's not likely a whole lot of 'color psychology' involved. It's more likely "Blue? Blue is nice. Sure, go with that. Done."
Can't speak for your other two examples, but according to a New Yorker article written in 2010, Mark Zuckerberg chose blue for Facebook not for any technical meaning or symbolism in the color but because he is red-green colorblind, and as he said in that article, “Blue is the richest color for me; I can see all of blue.”
This may also reflects founder's perception on their business strategy. Wheter they are aware or not.
There are 2 terms in business related to those colors: blue / red ocean strategy. Blue means that business focuses on creating completely innovative and new things, whereas Red Ocean Strategy means that company is putting all its energy into augmenting services or products that are already delivered by someone else - basically it more about fighting against it's competitors.
I think that some of those colors in brands logos may have origin in this - at least when it comes to blue color.
I have read research that says that casinos use reds and warm colors at the entrance to attract people, but use blues and cool colors inside to get them to stay longer. If it does have that effect, it may be another reason social media sites choose blue.