Technically eInk is the brand name for one brand of electrophoretic displays (see
http://www.eink.com/history.html), the one that happens to be used by all the major ereaders.
As for the Kindle's font, it is definitely a heavier font than the Kobo default fonts. Just compare the two side-by-side. I'm not saying that's good or bad, or whether it is optimized for the eInk display, but I note that heavier fonts on the Kobo screen also look darker and sharper, so that probably explains the majority of the font impression.