You might not run OpenBSD, but if you're running ssh on your Linux system, then you're actually running OpenSSH from the OpenBSD project. If you appreciate being able to access your systems more securely through ssh, please consider supporting the project by buying a CD set, tshirt or poster from them.
I'm not sure what you mean. Portable openssh is openssh + support for non-openbsd systems. This also includes things like pam support. I'd say that the "portable" part is almost all there is to the "portable openssh" project.
http://www.openbsd.org/orders.html