Font rendering is a dark art at common resolutions of ~96dpi. These displays are not really suited to display resizable fonts (as opposed to hand-crafted bitmap fonts). To render half-way readable fonts at ~96dpi you cannot just pre-render at an extremely high resolution and then downsize using a generic algorithm. (Even ignoring the unacceptable cost). To the best of my knowledge most fonts are only readable at 96dpi because glyphs have manually picked control points to make sure that certain delicate points are aligned to the pixel grid.
Wording amendment: ... that certain delicate features are aligned to the pixel grid.
Addendum: It obviously depends on the display font size, or more easily, how many screen pixels are used for rendering. The dpi is only an indirect factor. For normal screens on laptops and desktops (< 1m distance) typical font size means low pixel density. For example, the character '9' as rendered in my comment on the HN website has 6 horizontal and 9 vertical visible (coloured) pixels. Which means that Antialiasing (grayscale) is absolutely needed. Which again means that the borders are somewhat washed out, causing eye-strain.
The situation can be somewhat improved using subpixel rendering, improving the horizontal resolution by a factor of 3, optimistically speaking. Though subpixel rendering relies on the structure of display pixels, and that the monitor is not rotated, and it's hard to get right and some people will always complain about colour fringes.
