First, the default weapons are just as good as the unlockable ones. Most of the unlockable weapons are for fun, and they're often the weaker choice. I wouldn't care at all if Blizzard wanted to sell gear, if you automatically got a default gear set that was just as good as the store options. Second, while TF2 did have microtransactions added later in its life, it never had a monthly fee, nor DLC fees (Call of Duty, anyone?) for its updates. Of course, now it's completely free to play. Valve didn't have to do that, but it did.
Finally, why would Blizzard make WoW free to play? They've got defenders like you who are perfectly happy paying a monthly fee and full price for expansions, on top of all that revenue from "premium" items and services that are usually hallmarks of a F2P game. Without, you know, that pesky "free" part.
In any event, it's irrelevant whether WoW goes F2P in the future: we're talking about Blizzard's greed now, not some distant point in the future.