Something about the curved corners leaves me really pleased with how it looks.
But I wonder if Git's author's boorish-yet-sort-of-amusing behavior when invited to speak at Google a couple of years ago may have also quietly weighed on the decision some:
edit: To elaborate, we view the growth of DVCS in general as a good thing. (Also we have a big surprise coming soon for hg users.)
While there might be technological advantages to Python/Java/Mercurial, the Ruby and Git communities are a more evangelical and willing to try new things.
There's a ton of fantastic work being done in Python and on the JVM, and quite a few vocal fans of hg. I mean, Scala and Closure get a ton of play here. People are doing fantastic stuff with Django, Twisted, Stackless (and bragging about it). There are lots of people (me included) that would probably be using hg full time if it weren't for Github.
It's really important to keep yourself from being cloistered in a single environment, I think. It's awfully easy to miss cool stuff elsewhere if all you give a crap about is Ruby, and probably detrimental to your own learning.
I remember a large portion of Google's codebase has been based on Python/Java when Ruby was not popular back then. How could you say they made a bad choice to support their own infrastructure? As the reason of choosing Mercurial for Google Code, consider the following facts in addition:
0. Mercurial is written in Python (well, some critical parts in C)
1. Google App Engine supports Python first (then Java)
2. GvR works in Google
3. Python adopts Mercurial this year for version control
Looking at how github has exploded, and how much more momentum git has in the community, it's hard for me to be convinced that it's not worth the effort it would take google to support it. I also think they should support hg and bzr.
* Mercurial support at Google started before the discussion to move Python (I don't know details, but someone said it here so it must be true)
* Google was using Python long before GvR was hired.
[edit: s/hg/Mercurial/, I guess it's the proper thing to say]