I'd assume that it is so that lower level gatherers don't get completely shut out of a possible market, and gives them an item that is more likely to sell than some of the other stuff you can get. This at the same time prevents new characters being totally priced out of repairs to some extent as well, as I'm assuming the NPC prices (for the Dark Matter) will be 'ok' but not something you'd want to spend if you can afford it.
I'm definitely looking forward to it as a Botanist, as it means I finally have some kind of item that I know will shift, rather than having to do a lot of guesswork (and legwork!) I'm guessing the crafting recipes will be streamlined in much the same fashion (instead of needing x,y and z, you will only need x) and so people will be able to sell more as Gatherers, and Craft more easily as Crafters.
I'd also expect the number of items gathered (or at least the types) to drop quite dramatically - perhaps removing branches for only Logs etc. Also, I love the fact that the Materia system is quite widely accepted, and all it seems to be is some kind of 'magic goo' as well.