Saying that PS was never intended for photographers is such BS. How many years did PS exist before LR came on the scene? And yes, LR should definitely support files from non-Adobe apps. I don't use any such, but as you say, they need to support as many formats as possible for maximum success.
They *need* to spend their development resources on stuff that makes more people buy their wares. Same as any other software developer. They might have determined (rightly or wrongly) that the market for a catalogue-and-powerful-editor-and-print-and-web-and-... tool targeted at people who use their competitors' editor-and-print-and-web-and... tools is likely to not sell in huge quantities.