I got worried about supporting older OSes (there have apparently been changes to push notifications between 7 and 8). Probably not a necessary limitation, but as a relatively new developer I'm playing it very safe.

It's not an unreasonable choice given that most users are running iOS 8 or later:

9.X 0.1%

8.X 81.3%

7.X 13.5%

6.X 3.1%

5.X 1.9%

https://david-smith.org/iosversionstats/