Consider, as an example, the Mahalo stuff that started this. Jason's employee was given the opportunity to use his web dev skills on a much higher profile site and to work on a big open source toolkit (I assume he was referring to YUI or similar). Jason could either have wished his employee the best as said employee tried to take his career to the next stage, or provided him with some similar opportunity to convince him to stay, or... advocated for a system in which employees have difficulty switching jobs in order to keep the employee in an inferior position solely for the benefit of Jason. This is what Marc wants.
Note that in Marc's article, there was nothing about retaining employees by creating such an awesome environment that they don't want to leave. Oh, and btw? Here's a protip. If a dev in the valley making $100-$150 leaves for a $10K/year raise? It isn't the money. It's the boss. I claim that except for exceptional cases, salary is a 2nd or 3rd tier consideration for most great employees.
So, does Marc's advocacy of keeping employees by urging employers to systematically discriminate against people that switch jobs to find their best place that make him an asshole? In my book, yes.
ps -- protip #2? One way to discourage people from saying their boss sucked was to discourage it, ala Marc. The other way is to not be a shit boss. Again, Marc chooses the first path.
Sometimes people say stuff they don't necessarily mean 100% and before they know it they have already hit publish (And Google caches fast). For Mark, this is the first time I saw such a comment from him. So I am not going to hold it against him. I cannot say the same about Jason.