My experience with SVG is that it renders great in all modern browsers, but Illustrator, Inkscape and other vector graphics editors don't support the latest SVG features.
I suspect that's why Shutterstock asks contributors to upload an EPS file, not SVG.
I can point to SVG functionality (2 or even earlier in some cases) missing from both browsers and Inkscape, but my feeling is that there’s more missing, and more important stuff missing, in browsers than in Inkscape. Where browsers are generally ahead is CSS in SVG.
It's actually not been that hard to hand-write an SVG that looks good in the major browsers, but then Inkscape renders it into a mess. The areas I tend to run into it are when fine-tuning text, and when using complicated clip-paths. Maybe I only have this impression because I hand-write svg watching my progress in a browser, and only check in inkscape after the fact. Perhaps if I started with inkscape I'd be noticing all the ways the browser fails on inkscape svg instead. Either way it's not an ideal situation.
I suspect that's why Shutterstock asks contributors to upload an EPS file, not SVG.