Well Tapatalk use to be paid for as well, was cheaper than Pro/HD. I bought the original that now gone free. Not the 1st time this happened either, Splastop remote use to be paid for as well but the original paid version went free wen new version came out.
I got no problems with this either. I take it that the money I paid was worth it for the time I used it and see it the same as aging software on a PC.
You can not exactly add all the features for free till the end of time. So you need to make a clear cut and stop dev on older version with a branch for a new one. Its only fair to make it free if you stop adding new features/stop support.
I'll pick this model above the other one where dev's create DLC's like themes and charge extra for it. Tapatalk tried that, I am so glad they let that model slide.