Component quality is not going downhill. If you've noticed an abrupt change in DOA parts in the last 6 months, you should consider 2 things - logistics and ESD.
The biggest reason for DOA components is poor handling somewhere along the way from the factory to your door. Different delivery drivers, changes in routes leading to excess heat/cold/bouncing around in the back of the truck, changes in packaging from the retailer, etc. This is most prevalent with hard drives, but all components can suffer from it.
ESD (electrostatic discharge), however, is an increasing problem. With each successive generation of components, trace density gets tighter. The amount of voltage required to cause significant damage to a board has gone from several thousand volts down to under 100 volts. To put this in perspective, you feel an ESD shock at 3000 volts, and won't see it until much higher (8000 volts, if memory serves). Sometimes the damage caused by these shocks won't be crippling or obvious at first, but even partial damage to an electrical trace can be compounded over time by successive heating and cooling cycles. I've seen a few motherboards recently that have coatings on them designed to reduce ESD potential, although I'm not sure how exactly that works or how effective it is (nor would I rely upon that). Using a properly grounded ESD strap when removing components from their ESD bags is critical, as is working on a surface that is not going to hold a charge.
Also, avoid having open computer cases near cats. They uh.. they like the heat, and aren't afraid to jump right onto motherboards (sigh...)