Actually, it does make it hard. To do subpixel smoothing correctly, you need to be able to keep the total amount of color the same -- so if you want to move a part of the glyph right one, you'd light up a red from the next pixel right and turn off blue on the last pixel in your line on the left. This becomes both much harder and less useful when not all pixels have all colors.

But you are right on the other point -- at 800x480 on a 3.7 inch screen has a ppi of 250 -- or just normal font rendering looks as smooth as subpixel rendering on a computer screen, and I for one would be hard pressed to distinguish between subpixel rendering and normal when looking at text at size 10 or so on that screen -- just because I'd have such a hard time seeing it at all.

I wish we could get proper OLED computer screens.