As has been stated several times in this thread, the "swappiness" factor is not about over-committing RAM. It's about giving the kernel the freedom to say, "Hey, these pages in RAM have not been used in a long, long time. I'll swap them to disk so I can use that RAM for things that will speed things up more, like disk caching."
This is independent of applications whose working set size exceed that of physical memory.
Which then means that you're not allowing the kernel to make such decisions as what I described. (Rarely used pages paged out to allow for more disk cache.)
This is independent of applications whose working set size exceed that of physical memory.