Let's look at this from another point of view.. 

Let's say you worked hard for some number of years and paid cash for a brand new car from local "Dealer A".. plus each year you paid cash for their extended warranty or "Subscription".  
You loved this new car and drove it every chance you had.  You told all of your colleagues and friends about it, you drove this new car to new projects with your friends and held meetings about how it handles and how we can customize it.   Then out of the blue your local "Dealer A"  emails you that the title to your car will be transferred back to the manufacturer in three years time and you will need to then lease your car from the manufacturer if you want all of the new upgrades and still drive around with your friends. Plus too add insult to injury, over those three years they will be increasing your extended warranty by 5% the 1st year, 10% the 2nd year, and 20% on the 3rd year. 

By now most of us new car buyers have had to deal with this change in our beloved "Perpetual License w/ maintenance plan"  But the question remains. "Is it ethical to do what Autodesk has done?"

Tomorrow is not guaranteed and we know that life does not come cheap, but a contract should still be a contract?  Ownership is still ownership, or do we just simply lay down to the giant before us?