Does anyone know why you are limited to 1 chicken coop? You can have as many dairy farms as you want but only 1 chicken coop.
Chicken coops -- specifically the eggs that are generated from chicken coops -- are Zynga's chosen mechanism for doling out special embellishments to folks who are unwilling to purchase them with cash. Many things you hatch from eggs are run-of-the-mill, but sometimes you get lucky, and something special is provided, like a FarmVille float, an Acai tree, perhaps even the groundhog (though I haven't heard any reports of that).
Since the chicken coops essentially undercut Zynga's ability to generate revenue for FarmVille cash items in the marketplace, it is apparently in their best interest to carefully control and balance the flow of eggs, and that means controlling the number of coops. You'd expect that with two coops you'd get twice as many eggs, and so you'd expect twice as much of the special goodies. With three coops, you'd expect three times as many. If having additional coops were just a matter of spending more coin, like with additional dairy barns, then that would make it much more difficult to control and balance the distribution of eggs.
Now having said that, I don't know why they don't make additional chicken coops available
for FarmVille cash. It may be because the price would need to be pretty high, to correspond to the value of the special goodies from a second chicken coop.
Note that with dairy barns, they're not giving away the special goodies that are sold in the market for FarmVille cash. Instead, they're just providing a stream of calves, which aren't even "for you" but rather available for you to share with others, thereby fostering the collaborative mechanics that have helped make the spread of FarmVille viral. They are, of course, also affecting fertilizer, but again, that's not significantly impacting anything that would otherwise cost FarmVille cash. Finally, note that dairy barns are limited to five, unless you start paying for them in FarmVille cash.
I want one. 
