Why does easyWorship rely on the Average Weekly Attendance for pricing? Does choosing a high number of average weekly attendance mean we get a software with more features or is the software the same regardless of the weekly member attendance we choose?

Because you aren't buying the software, you are purchasing a subscription. They base it on attendance to help out the smaller Church's who don't have as big of a budget as the larger ones. 

And no, you don't get more features with the higher count. The software is exactly the same.

Thanks for your reply