NGK Iridium spark plugs

[Shifu]

ya i did have a look, they looked "ok" very white with a tinge of yellow, electrodes werent burnt, my comment about thinking it was running lean was due to the condition of the plugs, iv never had much to do with working on bikes, but being a car mechanic, white plugs have always told me lean, dark/black plugs always tell me rich, it never smelt of fuel, blew no smoke

That is a bit weird. You are right, the look you describe does indicate lean mixture - tad to lean. Going for even hotter plug should have made it worse. Considering that hotter plug improved the situation, could indicate that the high temperature look - whitish in colour, was caused by pre-ignition rather than lean mixture and the repeated shock waves were causing plug failures due to the cracking of the isolator. Hotter plug being able to absorb more heat was less prone to it (preignition) exending the life of the plug. Still a bit short from what you are saying. Normally they should last 25-30k without the problem. When something like you described happens it is always good to run some diagnostics as sometime things like that can indicate some other serious problems.
As far as the sparkplug "science" there is no difference really between the cars and bikes. Engine is an engine, so you can safely benefit from your experience with cars. I normally like my sparkplugs to be ligtly-brown gold in colour - getting hot enough to stay clean, but not hot enough to glow
The only difference are the two-strokes where the lean mixture can quickly lead to engine destruction due to lubrication problems.