Valve clearance price

[The Gecko_imp]

So what is then the main cause or process which makes vales "tighten up" over time, assuming the oil has always done it's work properly, and no knocking took place ? Are we talking about the famous seat recession, caused by the (too high ?) temperatures ? And what exactly is "seat recession" ?
I assume here that an engine like the CB1100's does not have "wild" cam profile which could also explain damage.