#13 - Jan. 11, 2010, 5:43 p.m.
As your fellow players have noted, Heirloom items possess an item level of 1. The item level for Heirlooms will not change based on the character level; it will always possess an item level of 1.
Because of this, any enchant which requires a certain item level above 1 cannot currently be applied to Heirlooms. Luckily, there are many enchants that do not possess an item level requirement (Crusader, Greater Stats to Chest, etc). It's best to seek out these enchants for your Heirlooms.
If you believe, however, that enchants should be changed in relation to Heirloom items, go ahead and drop a line in our Suggestions Forum. We'd love to hear from you. :)