Ummm... I think you can make that argument for ANY chart type. I can't differentiate between 25% and 24% in a bar graph either.

In fact, IMO, bar charts (normally) have the far worse problem of being relative to the largest value. In a percentage situation, you want the size of the bars to be relative to the whole, otherwise its misleading to say the least...

So the take away fact is that all visualisations have weaknesses under certain conditions.

But to offer graphing library that does not offer pie charts is, well, a bit silly in my opinion.