Using Taxonomy as Product Attributes

This page http://www.drupalcommerce.org/faq/product-attributes states that in order to use product attributes, "Add the size and color fields to the product product type. Their type must be List (text).". It would seem natural in many cases to me to allow use of taxinimy terms here. For instance, shirt sizes could be a vocabulary, common colors another. By allowing taxonomy terms to be used here, it would make it easier to cross-reference these things, e.g., providing a list of all "Medium" shirts, or all cloths of a particular color (regardless of wheather those are shirts, hats, etc).

Is there any particular reason why attribute types "must be List (text)"? Would it be possible to use taxonomy here? Or perhaps there's some even betetr way? It just seemed natural to me. But when I tried it out, I couldn't make it work so that for any fiven shirt the customer gets widgets to choose available colors, sizes, etc on the product display node.

-JM