Perhaps Tetris isn't as random as we think...

“Tetris doesn’t deliver the bricks in a completely random order; it shuffles ahead a set of bricks. If I recall rightly, about four sets of seven. What that does is it evens out the distribution, so it means you won’t get a load of S or Z bricks. You can’t possibly get more than say, seven in a row. These kind of tricks don’t make games worse, they put a lot of work into that and they believe that it makes the game better. I’m inclined to think that it does. But, it does isolate you from the brutality of true randomness.” - Martin Hollis, Bonsai Barber

This information comes from a larger article that takes a look at how randomness plays into the video game world. While I’m sure the information above is true for the earlier versions of Tetris, there have been so many new entries over the years, it’s hard to believe that someone didn’t tamper with that design a bit.