Blizzard officially call them 'Heirlooms'. Tigole:
You guys have discovered our Heirloom items. These (as you know) are Bound to account, which means you can mail them to any character on the same realm. They also scale with level. So you can mail these to a level one character and it will have appropriate stats (although slightly uber) for about 10 levels and then the item scales in power again, all the way up to how you're seeing it now.
We're also going to add some Bind on Account non-scaling items for higher level alts. in the future.
Sneaking in there with Build 8926's Paladin changes we have news of a new type of item, Account-Wide items.
These items are powerful items which can be transferred between characters on the same account. Their stats scale with level from 1-80 and appear to be roughly equivalent to Rares from that level. Some also provide a benefit in terms of +%XP for kills, indicating their niche as levelling items. They are currently bought with lvl80 dungeon badges.
The items themselves are slight variations on classic lvl60 items many of us will remember, such as the Arcanite Reaper or Herod's Shoulders, and use the classic item skin.
Hopefully we'll see more of these soon for all specs and classes. It's a great change, it just would have been nice to have seen them sooner.