" WE will never allow PvE to PvP transfer,"
Once BC hit, the notion that PvP leveling was "harder" was a bit overblown. The way the soloing experience is now, the difference is almost non-existent. Blizzard at the end of the day decided that the convenience of making it easier for friends to get their characters on the same server than maintain this fiction that leveling on a PvP server is harder than PvE.
As for Blizzard themselves selling items in the AH, I doubt it'll ever happen. Blizzard wants player participation in the AH. That's where there real money maker is going to come in for them: making sure there's a good volume of transactions.
Let's say for example, blizzard decides to release a sword for all players to buy. That sword will probably have an infinite supply, since Blizzard is the one selling it. Sure, blizzard will make quite a bit of money, but at the same time they will lose money from all the players that will no longer place their swords on the AH. After all why bother placing your sword on the AH when players are just going to buy the Blizzard one instead. Ultimately, more player fueled transactions will mean more money for them in the long run.
There's also some potential legal quandaries to take into account as well. Since Blizzard items would be of infinite supply, they would have an inherent advantage over player found items. Also given that Blizzard has immense control over how often items drop in the game world, this screams of foul play potential. This would be a market that is run by blizzard involving real money that would be potentially rigged in a way that blizzard items would have a huge advantage over player items. I'm not sure of what specific laws that would run afoul of, but I can't imagine that not causing some sort of legal problems.
As another example, let's say I find a super rare sword that regularly auctions for $2000. Then the next day as I'm about to put it up on the AH, Blizzard put up a sword with better stats that anyone in the game can buy for $25. I (and others who are in possession of swords that used to sell for more) could in theory sue Blizzard over that. We probably wouldn't win but the potential legal headaches probably wouldn't be worth it to Blizzard every time they released an item into their AH.
So don't worry yourself about blizzard selling items themselves. It probably won't happen.