One has to be careful when looking at memory usage to judge these kinds of things, though. Linux has a tendency to use memory unused by applications for its own purposes, because it's not being used anyway and it might as well do something useful with it.

Oftentimes this ends up being something like aggressively caching file data so that it doesn't have to write to disk very often. While this does get labeled as "used" memory, it can very quickly be freed up by the operating system by evicting this cached data back to disk if that memory is needed elsewhere.

This can make Linux appear more memory-hungry, but in actuality a better description might be that Linux is more effectively using the resources at its disposal. I'm not saying that this is what's happening in this case, but it's a possibility.