Earlier quoted context omitted.
My girlfriend does exactly the same thing. I wonder if its a gender thing? Her PC kept freezing, but she loves her new Mac Air.
I don't close programs anymore either, and I'm male. I do close documents to keep Exposé from getting unworkable, but my emacs usually has dozens of buffers open.
I dislike clutter and distraction. If I leave a Twitter client open or IRC I easily get distracted by it, so I'm constantly hitting CMD-W and use Quicksilver to open them when I need distraction. Same with iTunes when no music is playing.