Chrome constantly runs tests against thousands of the most popular sites to make sure they render right.
It's not the developers' jobs to make their sites work with Opera (especially when it works in IE, Chrome, Firefox, and Safari). It is Opera's job to make sure they render sites comparably to other leading browsers.
If that means they rip out their rendering engine and replace it with Webkit, so be it.
You obviously have no idea about the lengths to which Opera goes to get sites working.
Some quick references
i) They actually fix bugs on popular websites on behalf of the developers: http://www.opera.com/docs/browserjs/
ii) They actually have a position called "Web Openers", whose sole objective is to reach out to web developers.
iii) An idea about the kind of compatibility issues and bugs Opera has to deal with : http://my.opera.com/hallvors/blog
iv) An anecdote demonstrating the lengths to which Opera goes to fix broken websites: http://my.opera.com/ODIN/blog/2009/11/05/the-lengths-to-go-t...
Go through them and let me know if you still believe that Opera doesn't try hard enough. The problem is that being standards complaint is harder than it soudns. A lot of the nitty gritties aren't explained in standards and diff browsers implement them in diff ways. While developers explicitely implement patches for Fx and IE, they generally ignore Opera. And that's why so many websites don't work in Opera.
Sorry but its the developers job to code correctly, so that the site will work properly in the standards compliant browsers (Chrome, Safari, FF and Opera).
Coding wrong and passing the problem to the browser is just mean
BTW, different rendering engines, assure no monopoly, innovation and competence, which is always good.
It's not the developers' jobs to make their sites work with Opera (especially when it works in IE, Chrome, Firefox, and Safari). It is Opera's job to make sure they render sites comparably to other leading browsers.
If that means they rip out their rendering engine and replace it with Webkit, so be it.