It's been a pretty bad time for Martyn in recent times. Dropped (unfairly, many would say, including myself) after the Ashes, he's struggled to find that great touch he had a couple of years previous to that fateful Ashes tour, and he's succumbed again and again to that waft outside off stump in direction of gully - which is obviously a concentration issue he was able to control through his purple patch. Apparently he split up from his wife not that long ago too.
I wonder if this is a bit of a **** you decision directed towards the selectors in anger, based on his "losing friends" comment, seeing as it was obvious he would have been replaced for Perth had Watto been fit. Perhaps he thought they would replace him with someone like Jaques anyway, or maybe he found the thought that they wouldn't, and that they might play him at Perth with the idea of replacing him as soon as Watson was fit, insulting.
Ideally, while respecting his decision, I think he should have done this a different way, and announced his retirement while agreeing to play in Perth. Very few players actually get a "final game" at which to soak up the adoration and goodbyes from their fans, particularly at their home ground, and I think he should have taken that opportunity. Of course, it's possible he requested this and the selectors denied it, but if so, that would be particularly heartless given that he'd have every motivation still to do well at his farewell, and the Ashes are just about in the bag anyway.
Regardless, wish the guy all the best, he was absolutely instrumental (indeed, one of the chief architects) in our great performance on the subcontinent over '04, particularly of course, winning in India. Great aesthetically, and able to comfortably rotate between defensive and aggressive defending on the situation. Like quite a few other excellent players, his greatest enemy was often himself.