Google not officially supporting Opera is just like program developers not producing a Linux version in that they both have tiny amounts of market share and it potentially would be a waste of resources to fully support the little players.
I disagree somewhat. The browser market has IE, Firefox, Chrome/Chromium, Safari, Opera all of which are free to download. Also two of these are also open source as well. The majority are cross-platform as well. They are also all "feature complete"/"stable".
In operating systems, we really have Windows, Mac and Linux. All three are "feature complete"/"stable" at the kernel level, but one isn't at the GUI level (cough X on Linux cough). This one is the only free, and also open-source OS. Once somebody makes a move (thanks Valve), then the unstable parts will get the attention/funding it so badly requires - but many ***** out (or even get scared on the legal front). The point is, the infrastructure like buggy/incomplete APIs also stop development on this platform, not just because it has 1.5% of the desktop share.
Opera is in a saturated market where it isn't standing out in terms of license, features or standards support (though I know they stood out well in that department in the IE6 days - everyone is much more on level in that aspect now). Why support the rendering engine when it will need it own tweaks (which cost a lot of man hours), when they are so many other alternatives as well as the market share. Anybody can build a browser with Webkit or Gecko don't forget.