Honestly, I don't see this as a major problem. It COULD be if certain publishers take it in the wrong direction or set goals WAY too high (like the whole Dead Space 3 thing, the 3 million sales needed), but that's different to this preorder situation.
There will always be a set amount of people who will preorder, so that inital reward will almost always be a given. Strange how people are saying they're holding the other content "hostage" though; that would imply that it's something you already had that they're with-holding. That first group of content (if the percentage was reasonable) is the same as any other preorder, little bit of something that makes the game feel special without adding massive content.
TF2 bonuses... let's not go there.
A *free* copy of Civ5 is not being held "hostage" because at no point did they say "With every preorder you will recieve THIS". It's a way to entice those who wouldn't have normally preordered to seriously consider doing it. In this form, I don't see this as "evil" or "slimy salesman", it's smart marketting.