I'm not using any screen protector on my new phone (not yet anyway). I don't think it's an issue with screen sensitivity. How I see it, the issue is that in order to advance the screen left or right (say in an image carousel), I have to stretch my thumb really far over to the left side of the screen. If I don't reach really far over, and just do a lazy right flick instead, the screen registers the touch and moves right a little bit, but when I lift my thumb, the current screen just springs back into place instead of advancing to the next screen. It's most noticeable when viewing screenshots in the app store.
I did not know that about Magic Earth. I’ll have to test that out on my next trip into the city.