Its all about opportunity cost. For us to gain one advantage we have to sacrifice another. We can't have our cake and eat it too. I agree that if we were playing against cheiftain level AIs we would tech AH>Mining>Wheel>BW>Fish>Myst.
1. AH for Sheep pasture/ find potential horse
2. Mining for silver mines
3. Wheel for Immortals
4. BW for chops, potential Copper
5. Fish for scout wb and potential early contact
6. Myst for Stonehenge
We cant get all of these things at the time when we want them... We want sheep ASAP, silver ASAP, Stonhenge ASAP, contact with other civs ASAP. We have to put one priority ahead of the other. Making contact is more important than ANYTHING else. Really, it is more important than sheep pastures, but AH is also needed to find horse so we are teching AH first. If we delay early contact by even 1 more turn than that, we will pay dearly for it for the rest of the game.
For example, if the wb meets 2 other civs, we may be able to make a deal with them whereby they agree to let us get SH. We may be able to get NAPs and fixed borders in place, so that we dont need monuments or Immortals as urgently. If we don't get any of these things, and three civs are racing for SH by the time we meet them, then it may be too late. That is what opportunity cost is all about.
@ damnrunner - the mine is finished 1 turn later if we tech fishing so we lose 5

in excahange for a better chance to be the first team to meet an ally. 5

to meet an ally first seems like a good trade to me.
And the suggestion was having the worker spend a turn building a farm instead of just idling, but I guess the worker could just go straight to the hill and idle for one turn instead. I agree that finishing a farm would be of marginal benefit, that is why we would not finish it, but instead move to the hill the turn before mining becomes available.