Because if old became account bound the only way to tip a player who (for example) enchanted your gear would be for you to give them some flasks or a gem. If gold was account bound than you couldn't trade it and if you cant trade gold then the only way to buy stuff is with other stuff. Bartering.

*gold

Because if it is account bound, it is no longer currency, as far as player-to-player is concerned. He is talking about the fact that we need a currency of exchange to enable the exchange of goods from player to player, not just from player to NPC.

His answer is regarding the fact that it would no longer be liquid, since you could no longer give it to someone in exchange for something else. I think his answer addresses the question in that way.

I think the problem here is the term you are using. "Account bound" implies that the gold is tied to a person's account (much like "Soulbound" is tied to a character). I believe this is not really what you are proposing. It sounds like what YOU want is for gold to be exactly the SAME as it is now, but also AVAILABLE to all of your toons not just one at a time. I picture this as a shared bank kind of thing between toons, so you can avoid mailing money to toons on the same faction or, if you play both sides so that you CAN get money to the horde side without asking a friend to play the overpriced Grey Item auction game? Let me know if I am misinterpreting.

As far as level 1's, if they are on the same faction you only have to MAIL them the money.......That's not that difficult. The difficulty is when you decide to start an opposite faction toon and suddenly there isn't a way to mail THAT toon money. BOA items can be mailed to the opposite faction, so why can't GOLD that you have on your ALLIANCE toon be mailed to the HORDE toon you just created?