Welcome to WebmasterWorld Guest from 188.8.131.52
The G update is still going on (even though the threads are shut down), so I doubt anything you did to your htaccess file caused the drop. HOWEVER, I AM noticing that every time I add my 301 redirect I seem to DROP in the G SERP's. I remove it, and I climb back! This has happened about 5 or 6 times, and right now it's added. So if I drop again, then remove it, then climb back, I'm convinced that at least a 301 of non-www to www is hurting me. So, there could be, MIGHT be something to be said for the "Checkspelling" you did.
If you've had your htaccess file like that for a month or more, then you dropped, and that was several weeks ago and you are still dropped back, you may consider removing it for a few weeks and see what happens. Unfortunately it's all a waiting game for everyone.