The OP's description makes it pretty clear. This is a library that seems specifically geared toward those who create SVGs in programs like Illustrator. That it is described as "jQuery for SVGs" should imply that it serves a different need than D3, as one usually does not call or think of D3 as the "jQuery for SVG data visualizations"
The moment we start calling things "the jQuery of..." we're no better than startups that are "the Facebook of..." :)
This is a drawing lib, not a data binding lib. d3 is largely rendering agnostic. You wouldn't use them in the same way like you wouldn't compare contrast a car with an engine.
Agreed. And, I think it would be helpful (and increase credibility) for the Snap creators to include a comparison with D3.js at http://snapsvg.io/about/.