The current default is to display end caps on error bars.

I argue that end caps are not useful as visual cues for most plots. They are seriously harmful in "busy" plots with many data points, where error bars start to overlap and the end caps start to cross other error bars.

Tufte teaches us that we should maximize the data-to-ink ratio. End caps do not provide any additional information over the error bar, so they should not be there by default. End caps are useful to indicate a secondary interval, like the systematic uncertainty of a point, a beautiful example is Fig. 13 in this paper:
http://arxiv.org/pdf/1409.4809v3.pdf

I recently introduced a patch to make the default length of these end caps part of the configuration, so that they can be turned off by default (by setting errorbar.capsize to 0 in matplotlibrc). Please make this the new default. :)