I'll respond to your question about what font fms suggests for e-book reading: I use NokiaSans, 18 point, bold. But that doesn't mean fms does, nor that you should.
Likewise you're way off base supposing that screen size and pixel density don't "really" matter to us eBook readers. Maybe it doesn't matter to some of you (which amazes me, but if you say so ...), but I assure you that to many of us it matters immensely.
When you say eBook reading is a niche, I agree with whomever (fms?) said most Tablet uses are niches. That's what's so great about the Tablets: One Device, Many Niches!