A brief answer, without reference to any Dock: when I last checked, some of the perceived differences are not yet explained, not yet understood; and some of those actual differences (or differences in perception) are unrelated to normal use of non-Retina hardware.
Screenshots of OS X 10.9.5 attached. Our preferred orientations differ but in both cases I think the shadow is as it should be, fairly even around three 'edges' of the Dock.
For a designer's attention to detail, an eye that's far superior to mine, this chap comes to mind:
https://twitter.com/eli_schiff/status/492504341262004224
One of his more recent shots, of shadows around UI elements with very varied positions (overwhelmingly user-defined)
https://twitter.com/eli_schiff/status/526137695366418433 may help you to decide for yourself whether the shadow in your case appears proper for a single UI element with a much more predictable position (momentarily user-defined then infinitely system-defined).
Light, dark, shadow and headings
One of your other screenshots:
Image
That's the head to a (possibly empty) list of notifications, yes?
Without reviewing other recent points of reference in this forum: I see, first and foremost reading top to bottom, left to right the
bright 'Notifications' text shining through a
dark background. So whilst it's not in your screenshot, I expect to see bright text, on a dark background, below the heading with those same qualities.
Also: the button to the left is outstanding (standing out, towards me, not pressed in towards the screen).