Welcome and thanks for writing this.
I think you are right to consider what you are paying for in this way. Although perhaps not stated officially, I think some of the things Purism are doing/selling are meant to generate income, pure and simple. Probably the additional memory charge is one such thing, there are also others. If we think about it, as you have done, it’s not really strange. Purism are doing some important things that need resources and the money needs to come from somewhere. (Unlike some others they will not get funding from Google et al)