Consumers have this "price of lunch" mentality and will spend the money without realizing how there were 18 civs to come with civ v and $5 per DLC civ is clearly a ripoff if they'd do the math.
Thank god people can choose if they want to be ripped off

I can do the math, and I choose to pay for the DLC.
Some people, like me, find it worth $5,-, others don't think it's worth the full $5,- and wait for a sale when they're $2,50, and again others don't find them worth any money at all and don't buy them.
Just like some people bought Civ 5 on Steam for $50,- where other people, like me, shopped around and only paid $30,- (that's 4 free DLC

) and again other people waited until it was on sale for $8,-
It's just what the customer wants to pay for it.
I think Camikaze said it best earlier in this topic:
[...] but whether you consider a civ worth $5 depends entirely upon what else you'd do with that $5 and how much enjoyment you actually get out of the new civ. [...]
And I think that's the core. It depends from person to person what they could otherwise do with that $5,-.
For some people it's not even lunch or a beer, for others it's more significant than that. Also it depends of course on the amount of enjoyment somebody gets out of it.
Although this is a more pragmatic view and less principal view than yours, though

And can understand your point of view though, I just don't fully agree with it.
Mind you, it does help that I view the DLC's as a smeared out expansion.