You're just making that up.

The Scourge didn't know about Jaina's exodus to Kalimdor. They were busy with Lordaeron, heading >north< into Quel'Thalas. That's the opposite side of the continent. All other nations are left untouched from the plague.

Secondly, Stormwind harbor isn't being built. Stormwind was already fully recovered, by funding of the other nations. They are only making a second Gatehouse (entrance, tunnel) for us players to enter it. The harbor has always been there, just not added yet ingame.

As for the Legion, they weren't after Jaina and Thrall. They were heading to the worldtree.

Stop making up stuff mate :)

Mannoroth was after Thrall, or the orcs in general, in anger over them failing him? Or did I dream the bit where Tichondrias mocks him for his failure and he decides to take his anger out on the orcs?

As regards Jaina, I wasn't talking about the reason for her decision (clearly that had more to do with Medivh) but was arguing against what good it would have done if she had fled south instead. Stormwind was not a fully stable kingdomyet, though the defias timeline isn't set in stone that I'm aware. I'm not in LK beta but I've seen no evidence of any other entrance to the harbour to indicate that it's in common usage (if it is, where the hell are boats going - because it's not anywhere in the Eastern Kingdoms or on Kalimdor!)

After going north, the scourge went south to Dalaran. Do you honestly think they would have stopped there if Tiochondrias' death hadn't given Ner'Zhul the opportunity to fortify his strength in the north in a bid for freedom from the Legion's control instead?

So I'll concede that Jaina's journey south would not in itself cause the scourge to follow, but I'll remain stubborn on that escaping over the sea was a better option given the defensive options the southern journey would offered.