What is wrong with pdf?

[ghostwheel]

Why do pdf files display so badly on the reader? When I take a text and put it on the reader in RTF form, letters are crisp, and I can easily read the text at "small" setting, with ~80 chars per line.
When I look at a text pdf (i.e. not text converted into an image), the text is very faint. Bold text looks black, but regular text looks gray. Only text with quite big letters can be easily read.
Why is that? Is it really that the reader displays regular text in pdf files in gray, and only bold in black? Or are the fonts used too thin, and only thicker fonts display black because of anti-aliasing?

[NatCh]

Originally Posted by ghostwheel

Or are the fonts used too thin, and only thicker fonts display black because of anti-aliasing?

I think the last general consensus was that it was a combination of those two details, but I don't know that anyone has a definitive answer.