Supposedly there's a huge amount of people who pay money to transfer characters for the sole purpose of moving heirlooms to different realms.
I really can't imagine there being enough people doing that on a regular basis to matter.
Actually, my wife and I have done it more than once on both of our accounts. We'd move a low level alt with all the heirlooms if we wanted to start from scratch, or a main we desired to with all the heirlooms otherwise. What always sucked about this, is when you have 30+ heirlooms and you miss one somewhere. At one point, I did have every heirloom available, and I missed the agi mail shoulders in a move.
I believe they are putting in the x-realm mailing before people bitch about enchants ... some don't have them or don't care, but others have some relatively expensive enchants (agi ones I believe were always quite expensive because hard to attain mats [wind essence?]).
I think it is great they implemented both; but I can understand the sour taste for some after years of saying 'we can't do it' to magically doing it (in a vacuum, ignoring the realm mergers).
wish I could refund a couple duplicates I have before this goes through in WoD