Yeah having both enlarged side-by-side, the difference is that generic "shiny button effect"
When I wrote the last post, I was going by memory and didn't even remember that the old logo did use this effect though, I just noticed that there wasn't shadow/midtone/highlight any more, only midtone/highlight -- that's the actual issue I meant to raise.
The shiny button effect itself isn't necessary, but to break down what it does in the old logo -- the "half moon" section at the bottom of the circle becomes the shadow part, with the rest of the circle being the mid-tone, then a circular highlight is applied over both. It's not that particular configuration of shapes that I remembered, just the fact that it used a palette of 3 colours in the effect.
Even the outer ring of the old one has a shadow at the bottom right to add some depth by contrasting against the brighter top half of the centre circle.
There's also a subtle hue change between the two logos (the new one is much more green/teal than the old one), and the choice to have the glyph cut through the outer ring.
 Also, the new one's centre circle isn't exactly centred, with the width of the white void differing in places, and the circles aren't anti-aliased as well (in both high and low res this is noticeable).