But when a lot of miners "cashes-out", then the bitcoin client will automatically lower the mining difficultly level based on a hard-coded protocol.  Since it will now be easier to mine, then that means that other people, including noobs like yourself, would be incentivized to mine at the easier difficultly level, since the bitcoin payment for solving a block would remain the same (50 BTC/block solved currently).

No problem.  Again, I had similar concerns when I was a noob as well.  Anyway you get a gold star in my book for using Ubuntu Linux and for asking simple & clear, but non-trolling questions/concerns.