My guess is they are selling their membership opportunity they are currently being offered through Adobe because they own CS6. Just received the email myself within the last week because I am still using CS6 and Adobe wants me to change over. They are making money on it. The cost for me is $29.99 US/mth for the first year.
Not sure how exactly they are getting away with it. Also have a look at their feedback and you will see that they have no feedback relating to any kind of sale of this kind before. I would certainly not buy into it. I would hate to run into problems down the road and have Adobe tell me that I actually don't own the subscription license to the product.