Exactly, mostly 'cause I'm too lazy to stop and buy some. But in the end I probably keep 50% as "I'll visit this later" rune which ends up having 1-3 vendors that are empty.

And here I always thought someone was just throwing those away...
kidding...

Whatever is on the ground at Luna bank is a free for all. However, I've seen some runes renamed in obscene things, and that is something I have an issue with.

That's why I mark actual house runes for my vendor shop. Those can't be renamed. They can be marked over, but can't just be renamed.

I too have seen people rename runes with obscenities. (Well, I've seen the runes themselves - I've never actually caught anybody doing it).