These assume that in the end they want all gamers on their system and not a sub-set (even if that sub-set is huge).
Nintendo - online, too casual an image for some, not enough horsepower for certain genres, too weak/competitive relationship with third party developers, completely missed, or didn't care, about big swing in West towards PC style genres on console, question mark over their ability to 'bottle lighting' twice in a row.
Sony - poor marketing and overly confident early on, too slow in general (with online, with using their assets, with getting core franchises too market, etc) too unfocused in how they bring their offering together and missed the huge swing to Western style PC genres on console in US and to a lesser extend Europe, bit of a mixed image right now, halfway between Wii and 360, looking a little lost following Nintendo for motion controls and MS for online and too often tempted to use consoles to push other company agenda's - for example storage formats
MS - too reliant on online/hardcore Western titles focused on US, too weak in 1t party capability, overly reliant on third parties, wrong image for more casual gamers, poor peripherals strategy, possibly over banking on Natal's success, need to fully shrug of RROD image. Saw, indeed arguably started, huge move in US away from PC for online gaming for FPS and similar genres, but ended up overly 'typecast' as a result