Gaming reddit has become something of a fun challenge that a large amount of people are trying to do. Their success rate is probably far higher than any of us know
It is incredibly easy to game reddit, and the temptation to do so gets stronger as the site gets increasingly iron-fisted about the 'not mine' policy toward original content. I don't, though, because I feel dirty doing it.
Think about content on a spectrum from 1 (awful) to 10 ("best of"). Most of the content on the front page is about a 5, 6, or 7. But most of the content not on the front page is a 5, 6, or 7 also. What's determining whether something reaches the front page isn't necessarily the qualify of the content, but how many upvotes it got to start with.
If you had, say, 30-40 IPs you could use to give a link or comment 30-40 upvotes within a short time-frame after that link was submitted (say, two hours) then that link's chances of rising to the top of the front page would be something like 1-in-10. If it's any good, your chances are even higher than that.
In '07 or so, I tried to submit some links and they'd sit in /new only to be downvoted by the three people and never seen again. So I decided to conduct an experiment: I had a router that gave me a new IP every time I reset it, so I just used this to get ~30 different IPs and gave that many unique upvotes to a link. At that point I didn't need to do anything else: the link skyrocketed to the front page.
This works for comments, too, by the way. And as I'm sure you've noticed, this is what 'brigading' is in essence, just with multiple people.
I've called this Upvote Padding. Most of the people who are "gaming" reddit aren't actually forcing something to the front page with thousands of upvotes; rather, they're giving their links a tremendous head-start and letting a herd of redditors stampede it to the top because their view of "good" and "bad" is too influenced by the pre-established views of others.
So I'm almost certain that major companies are doing this for the front page. If I was able to do this in 2007 with a single router, I can't imagine what corporations who may have access to thousands of available IPs are doing.