Specially coated means, to protect from stomach acids.

NOW also makes one that is a bit more affordable.

http://www.iherb.com/Now-Foods-P-5-P...60-Tablets/740

http://www.iherb.com/Solgar-P-5-P-50...-Tablets/12335

The word encapsulated typically means that something has been put into a capsule. It can be used to describe the tiny time beads found in some long acting products. The little beads are coated individually to change dissolution rates. It might be interesting to open a Metanx capsule and see if there is a little enteric coated pellet inside, containing the P5P?

Back in the olden days!!!... Darvon compound-65, which was a combination product capsule, had a pellet inside mixed into the powder. The pellet (the Darvon part) had a coating, to protect it from the aspirin that was in the powder. At that time I worked in a hospital and we had to make up placebos of Darvon Compound-65, for a specific doctor on the OB/GYN wing. He had many Darvon habituated patients, and typically used the placebos a day or two after hysterectomies. So we emptied out the manufacturer's capsules--removed the pellet, -- and replaced the contents with lactose, leaving the aspirin/caffeine intact.
Darvon was finally reformulated to remove the pellet:
http://www.leagle.com/xmlResult.aspx...985&SizeDisp=7
It became Darvon Napsylate..aka Darvon-N

The amount of magnesium in NOW's brand is really small. 75% is magnesium oxide, and that is not absorbed. It is too small an amount to be really laxative as well. A typical oral magnesium oxide laxative (Phillips brand caplets) is 500mg.
100mg ----of magnesium oxide 75% and mag taurate 25%.
No mag from the oxide will be absorbed and 25mg of mag taurate is a very small amount. But it looks "fancy" doesn't it?
Manufacturers do this to "beef up" they supplement lists to look more important. Many less reputable places use "proprietary mixture" to get away with not putting ingredients quantities on the label. NOW doesn't do that, thank goodness.

I suspect the magnesium is in there as a filler. There isn't much left to use as an inert filler when so many items are listed as NOT included. Magnesium also is used as an anticaking compound to improve flow of the powder inside the tablet pressing machines.
Magnesium stearate also serves this function. Both are not absorbed and instead pass out in the stool.
http://en.wikipedia.org/wiki/Anticaking_agent

Most people replying on "reviews" do not have chemistry/biopharmaceutical training. Please keep that in mind while reading them.