Here is my stab at it: Maybe the "recently" is that as Summer has passed the
rate of defective units has not slowed--and maybe even increased, especially in the lots of units sold/manufactured in 2005? The 3-5% could have been "out of the box" defective rate, but the continued breakdown and malfunction of units 6 months (and counting) later defects have appeared that are more significant of a trend. Thus the new extended warranty for 2005 units and noting that recently the defect rate of units has increased instead of leveling out.
I don't have any further information than anyone else, but based on the memory shortages it could very well be that Samsung/et al were verifying memory with razor sharp margins of error, MS used it, and long term more units than expected have broken down than expected.
All conjecture of course, but I think more likely than some of the theories (especially those with more sinister intent... not that you are suggesting such). This is one of those delicate situations, and with 2M units in 2005 and a 5% initial defact rate that is 100k bad units right off the bat. Obviously MS has already had to fend of some crazy theories like 50% defect rate, so how do you approach the issue without lending creedance to the loons? MS made the right step by extending the warranty--on the negative they waited waaaaaaaaay to long. 1yr warranty should be STANDARD anyhow