I buy a comic book for $4 it's mine forever. I buy a digital copy I only have it so long as I maintain my account at $5/month or whatever the rate is.
I'm not sure about other services, but Comixology does not charge any type of monthly fee and the app is free.
I do however understand the concept of wanting paper vs. a digital copy. I guess it all depends on how you define ownership. An analogy would be photos on your PC vs. having them in print in your hands. Which is "more" of an ownership? The answer largely depends on your perspective (I don't think there's a "right" way to feel about this, it's personal).