Nutrients, and Effects of Raw Straw on Soil

The entire article can be found here.
http://www.americaslongleaf.org/media/2490/llp-management-for-pine-straw_nc-co-op-ext._.pdf

To summarize, less than half of 1 percent of raw straw is nutritive. This has a significant cumulative effect on pine stands which are raked regularly, which decreases tree growth and health unless the stands are fertilized. But the added nutrients to the garden using straw mulch are minimal, primarily increasing the acidity of the soil.

Breathability
The accumulated layers of decomposed raw straw form a thick blanket of thatch. Applications of insecticides and fungicides are absorbed by the thatch rather than the soil and plant roots, requiring that as much as twice the chemicals are required for effective treatments. This thatch also impedes the flow of air and moisture to plan roots. In low-rainfall areas, plant roots grow up into the thatch rather than the soil.

Insects
The thatch also provides an ideal environment for roaches, termites, and ants. Termite traps used by pest control companies consist of moisture, cellulose, and darkness, because this environment attracts termites. Thatch blankets provide the same attractive environment.
Because synthetic straw does not decompose, it remains permanently breathable. Because it does not absorb, water and chemical treatments go where they are targeted, meaning that a lower application amount is effective.

Synthetic straw is 100% sterile: no mold spores, pollen, weed seeds, insects, sticks and pinecones.