I've got only one route defined "xxx/:lang/:action/". Request of page / or /yyy should result in exception and the ErrorController to take control. But the page opens OK, despite that I have called $router->removeDefaultRoutes();. I just can't figure it out, how do I make any request, exept the ones that start with /xxx to throw the exception

Comment this line: $router->removeDefaultRoutes();
I think it's some bug in ZF. You are being redirected to index/index. According to docs Zend Framework: Documentation
this code should switch between exception and default controller but it isn't.

$front->throwExceptions(true) + $router->removeDefaultRoutes() = index/index
$front->throwExceptions(true) + #$router->removeDefaultRoutes() = exception

Thanks for response.

Yes, I am being routed to index/index.
None of the combinations of the three config options mentioned above do the thing.

Framework version 1.5.2.

Check this: [#ZF-3465] dispatcher - error when removing default routes - Zend Framework Issue Tracker