It seems like you can only do one cooking & fishing daily...is that supposed to be that way? I was trying to do the one in both Darnassus and Stormwind but once I did the one in Darnassus the one in Stormwind wasn't available.
For Cata dailies, yes, you are limited to one per day. The different cities simply offer a choice should you not like the daily offered in your current city. There are also achievements for completing them all I believe.