Xine-xvesa is built this way as to not interfere with other Xine extensions, and same with Pysolfc. I needed a certain lib built a certain way for pysol to run so I just put it in the extenison itself to get loaded. And since pysol remains self contained into it's own directory, it works equally well with either python-2.5 or python-2.6 installed. When pysol is installed into /usr/local with it's installer, then it can only be used with the version of python it is installed with as it resides then under /usr/local/lib/python-version. I would rather avoid having to rebuild apps when library versions change when it is possible.
If you build a self contained application installed into it's own directory, you don't have to worry about it conflicting with other extensions and you can pack in needed libs that will not conflict with other versions of those libs in the repo. As we have seen the headache of dealing with and updating openssl versions, I am personally going to either build statically against openssl or include the openssl libs I built against into a special directory in the extenison and use LD_LIBRARY_PATH to find them in preference to /usr/local/lib. At least for small, simple apps. Not all apps take to upgrading patchlevels of openssl and if you include your ssl libs in your extension in a different directory than /usr/local, then you will never have to worry about openssl version changes. This works with apps, though I know that with libs like qt it is not so easy and would just have to use the version found in the standard path. Of course, this is not meaning that openssl will be built into it's own directory again, but that I will include the libs I built against in the extension itself to avoid future conflict and reduce the openssl dependency.
#Clarification, only apps that will never be used as a dependency of others, or there could be the issue of 2 ssl versions if there were libs bundled with a dependency. Packing ssl libs into an app that has dependencies that also rely on openssl is perhaps asking for trouble. Better to use the standard openssl extension as a dep or build statically.
This approach works well with the current tcz extension type, though it could also allow the simple mountable app that does not require it's files to be symlinked to the system. And to me probably the main advantage is being more independent of other extenisons in the repo and avoid having to rebuild the extension when lib X or Y is updated.