I dunno about by default.. Maybe in the repo's. It seems ubuntu server is targetted towards advanced admins at the moment who don't want anything installed by default. So +0 for now.
The only way we have to install things 'by default' when something else is installed is to 'depend' on them. One could have php5 'recommend' APC; depending on ones options, that could have the effect you're looking for. Getting it into the repos would probably be a better place to start, though.