If you grow from 10 to 15, 20, 25 etc., each time, even though you are adding 5, it is a smaller percentage of what you had. In this example, you would be adding 50% to go from 10 to 15, then 33% to go from 15 to 20, then 25% etc. Growth is linear, but growth rate is decreasing.
Is that common terminology? It sounds like you're defining "growth rate" as "exponential growth rate." To me, if you're seeing 10, 15, 20, 25, etc. every month, then your monthly growth rate is a constant 5. You're still growing, it's just that your growth every month isn't a function of your size last month.
... whereas if your downloads per time month is a constant proportion of your total downloads to date, e.g., next month the downloads will total 2.5% of the total downloads to date ... and that keeps happening every month, then:
* the per-month downloads will grow exponentially as you graph it over time
* the cumulate number of downloads to any given date also will grow exponentially
Isn't linear growth associated with constant growth rate? Serious question, I'm not sure if I'm not missing some understanding here.