You've got to remember that all our reviews are comparative and based on performance-per-pound.
At the 37in screen size, the PX80 was/is a no-brainer: exemplary with SD, great with HD and with cracking contrast/blacks its LCD rivals couldn't match. And all for an incredibly competitive price.
However, move up to 40-42in and it's a whole new world: for starters, SD is having to be scaled up to a larger screen size, plus you start to notice the difference more clearly between an HD Ready set and a Full HD set when running Blu-ray content. There's also a lot more competition.
So, in short, the 42PX10 is a superb entry-level plasma that can take on the best in its class for TV broadcasts, contrast/black levels and value - hence the five stars.
However, at its price level and resolution, it's not going to have the sharpest edges or very slickest motion - for that you'd need a higher-spec model.