Blocks aren't a fair measure of someone being a good or bad turker though given that they are recommended by amazon for preventing retakes. People getting it while suspended makes sense if they are checking the work of a "golden" batch the person did /before/ they were suspended.
I'm not saying it's
not random, but like
@aveline said, we don't have all the information so just because it looks random doesn't mean it is.
Even though I do agree personally with the fact that blocks shouldn't be a fair measure, it is a fair measure for them to suspend people.
Just one example is mordea that got masters with the last round, and then was suspended just a few months later for blocks that he got prior to becoming a master.
So if they can judge the quality of someones work by blocks enough to close out their account, then it should tie into if you should be a master or not.
Or, of course, mturk is just incompetent when it comes to these things and that just makes a person lean towards "random" more than not.