I think there's only two types of oregano, unless you include marjoram in that little family.
I planted greek oregano because I wanted to use it in Italian dishes. (Ok, that SEEMED to make no sense, but it's the greek version that is used in Italy. And here as well a lot).
I found a little info on this herb and how it also grows in hot climates (along with the Mexican oregano), since you're always so kind to provide links and info, Eagle: here
From the link:
Those little hairs on the plant's leaves and stems are an indicator of what the climate is like in its home town. The hairs provide shade for the plant and slow down transpiration ( or water loss) from the plant. This allows the plant to survive some pretty hot, dry weather. The more of these little shade providers, the grayer the plant. That is why many gray leaved plants are tops on drought tolerant lists.