I personally think that its a little subjective how often one would strip down a setup. I believe it really depends on riding styles, type & range of equipment and also sometimes events.
I personally do freeride and XC. My FR (mostly street) setup receives more attention due to the abuse I put it through (i am heeavy!) - though, I dont usually strip it down that much as compared to the XC. The XC has been through all kinds of mud, dirt and sand so naturally some of them get into areas where the sun don't shine (:)). I strip the XC down probably every quarterly but there are quarters that dont see much action where I didnt (eg really rainy seasons with no chance of heading for the trails).
Type & Range of equipment
Higher quality equipment usually would require less maintenance but that holds true only on some parts. Most modern rotational parts comes with sealed bearings so trying to clean those up for performance are preety much futile (easier to just buy and fit a new one- like bottom brakets).
You would almost always want to strip down and give a full service to your ride when you are nearing a race where its critical that it performs flawlessly. Though do remember to do it a few days before so that you have a chance to readjust the fit/feel of your bike to you OR to change out parts that were found to have been damaged, worn out or need replacing (hangs on how much cash you have, parts availability and the like)