If they've respect for the dev they don't and let him make some money for his work and wait for public release. But yeah, respect on a pirate site... not gonna happen.
In a way I can see what your saying but I would say at worst he might lose a handful of of lower tier people cause if someone was willing to drop over $50 to get the game early it's more for support than playing the game early imo. I can't wait to get my hands on the game but I have to save so at most I could have done one of the lower options and I am sure there are a lot of others that think the same.
Not to mention how popular this game is I would likely bet it's a very small fraction they are missing out on, but the word of mouth traffic he gets from people on places like these easily makes up for that well again this is all my thinking. If I thought the dev was barely getting by and releasing here was costing them like 20 to 40% of their profit I would be there with you I just don't see that being the case maybe I am naive but that is how I see it at least.