> Almost agree ;) It's basicly imposible to distribute linux software as an ISV
If your goal is to distribute only one "universal" binary, you are right this is seldom possible. If on the other hand you start from source then it often just works or with only a minor effort.
Porting your source code from one Unix vendor to the other was generally much more difficult than from one Linux distribution to the other. Simply because Linux distributions share most of their underlying source code.