In Chrome and Firefox (and probably IE) right now, .getCTM on an SVG element returns the same results as .getScreenCTM (as far as I can tell).
From the spec, I can’t figure out why this should be - it seems redundant and pointless to me. I think it would make more sense to define el.getCTM() to return the same results as el.getTransformToElement(el.ownerSVGElement).
Possibly relevant Firefox bug: https://bugzilla.mozilla.org/show_bug.cgi?id=366697