My 2 cents on this is I think it is fair and understandable. You are fulfilling to your existing customers what you sold them and the need for more cash inflow so you can hire more people to maintain and upgrade the product line will only make the software better. As stated, this effects none of us long time backers. It is rare these days that a software company goes out of their way to make sure that their existing users base is not effected by changes like this.
To anyone that does not like this the answer is simple, buy your key NOW and as stated none of this will apply to you.